Sapwood Shipping and New Release of a Japanese Version of The New IPA!

I thought I would put together a quick post to let people know about a few updates in my world including a new shipping club with Sapwood of mix-fermentation beers and the release (paperback and e-book) of The New IPA in Japanese!

Sapwood Shipping Club

If you live outside Maryland and have been curious to try some of the beers from Mike and myself at Sapwood, we just launched a shipping club administered by Tavour that will ship to 34 states! The club will focus on our mix-fermentation bottles, but if you are interested in trying some of our “clean” canned beers, Tavour also takes periodic pallets from us that will show up for their single-can sale options which are separate from the Sapwood Club! These can include anything from IPAs, DIPAs, pale ales, Smüzí fruited sours, imperial stouts, and lagers!

How the shipping club works:

Two to three times a year, Tavour will ship a box to your home that contains six bottles of six different 500 ml mix-fermentation bottles. Each box will cost $146 which includes shipping, but you can cancel at any time. There is a limited number of spots available for the club, but a waiting list will be created after it’s it’s full! 

First Beer Shipment Box Includes:

Jammiest Bit: Our homage to Kriek and Framboise, a barrel-aged sour on loads of sour pie cherries and red raspberries. Fruity, funky, tart etc.

Barrels of Rings: Our pale ale base, mixed-fermented in wine barrels and then dry hopped right before bottling. Citrusy-funky with restrained acidity. This one is a personal favorite of mine!

Botanicia: A blend of pale sours aged in gin barrels that we then infused with dried limes and quinine. A weird play on a gin-and-tonic… but with a lot more acidity and funk!

Elliptical Orbit 2023: A continuation of our annual dark sour. For this one he roasted Geisha coffee beans and we infused the barrel-aged dark sour with Geisha cascara (dried coffee cherries).

Fruit of Many Uses: We sequentially racked the same barrel-aged tart/funky base onto second-use Chardonnay wine grapes, cherries, raspberries, and white nectarines. All of the fruit was whole/local.

Shipping available to: WA, CA, OR, NM, NV, CO, MN, NY, DC, CT, NE, MA, FL, PA, NH, NJ, ID, TX, KS, IN, WI, MO, IA, IL, MI, ND, VA, RI, NC, SC, MD, LA, GA, TN

If you don’t already follow Mike’s blog (The Mad Fermentationist), you should because he’s planning on writing up each beer included in the club so you can follow along on the recipe, process, and what we thought of the results (and what to potentially improve). Mike’s back to blogging! 

Sign up for the Shipping Club Here! 

The New IPA in Japanese

I continue to be amazed at the interest in The New IPA around the world and in the U.S. four years after its release. In English copies, it’s sold well over 20,000 copies to date, about 19,950 copies more than I was anticipating! In addition to the English version, the book is now available in Spanish, Portuguese, Polish, and as of this month, Japanese!

For the latest Japanese version, I have Kiyoshi Takoi, Ph.D., to thank! Kiyoshi’s official title is Senior Research Brewer Product & Technology Innovation Department SAPPORO BREWERIES LTD. However, you may recognize his name from his amazing work in the beer literature world. I reached out to Kiyoshi when researching for The New IPA back in 2017 and 2018 to make sure I understood his work correctly and to ask follow-up questions on how brewers could practically use some of the results from his papers. To get an idea of how much Kiyoshi has contributed to the beer knowledge world, a quick search of his name on Research Gate shows results for 74 published papers with his name as an author!

Kiyoshi reached out about a year ago to see if he could translate the book and include a new Chapter from a Survivable blog post; my answer was obviously, of course!! Those in Japan can purchase the book from Amazon here.

Researching, experimenting, and writing about biotransformation has been one of the most exciting and frustrating topics to cover over the past few years. I have brewed batch after batch of beer, attempting to piece together research from the wine and beer worlds to unlock the true potential of hops and fruit. Whether it’s incorporating wine strains as a blend with ale strains to unlock bound thiols hops (the same thiols in wine grapes like 3MH and 4MMP) or doing solo ferments with wine strains like Vin 7, QA23, 71B, and the Alchemy blends (scientifically formulated to be strong biotransformers). 

Except for one trial I wrote about, where we experimented with wine yeast and a lager strain, none of the trials were good enough to scale up to anything I would be excited for people to purchase and drink. Although sometimes interesting, the result of these trials is often fermented with strong phenolic characteristics masking any unlocking of thiols that may have occurred (even when some of the wine strains were less than 10% of the total yeast pitch). It’s also likely that, although these strains were great at releasing bound compounds in grapes, the nitrogen that is in excess in the wort and limited in wine ferments, can inhibit the beta-lyase activity in beer ferments and ultimately reduce the number of unlocked thiols. 

This cycle of excitement and letdown with my thiol chasing trials is part of the reason I was so interested in the work done by Omega Yeast and Berkeley Yeast this year in engineering yeast strains designed precisely for biotransformation. Using CRISPR technology (at least with Omega), they are now able to create hazy IPA yeast strains that, like many of the wine strains studied prior, have the necessary gene (IRC7) to produce the required enzyme (beta-lyase) during fermentation to unlock thiols. 

The advancement in engineered yeast is exciting because now there is some potential to achieve higher thiol concentration in hop-forward beers without the clashing phenolic yeast fermentation characteristics that I was getting from the wine yeast trials. But, to increase the chances of unlocking bound thiols, the engineered ale strains not only have the IRC7 gene (for Omega yeast) or TnaA (for Berkeley yeast) required for beta-lyase activity but it’s overexpressed. Essentially, this means the gene activity is turned up or highly expressed, allowing for an even greater release of bound thiols. If a strain has just a functional beta-lyase gene, it may not be enough to reach sensory results without this overexpression. 

Rather than getting into a lot of technical text (most of which was covered in a previous post on bioengineered yeast strains), below is a flow chart of sorts that helps explain how and why their power in unlocking bound thiol potential in hops. 

This post covers how brewers might be able to use new products (like Phantasm powder), new techniques (like mash-hopping), and how to experiment with high thiol-bound hops. Also covered in the post is Sapwood’s collaboration beer with Omega Yeast and Phantasm (along with thiol test results from France), current understanding of thiols, and how we might be able to use the science to achieve higher thiol concentrations. 

Phantasm Powder

It’s not just hops that have an incredible amount of bound thiol potential, but wine grapes (and other fruits) can have lots of bound potential, which is where most of this research started in the first place! A new product that has begun to find its way around to breweries and Instagram is called Phantasm. Essentially, Phantasm is an extract of New Zealand Sauvignon Blanc grape skins processed into a powder that can be used at various points in the brewing process. Even after being used/pressed in the wine production process, the wine grape skins can still contain bound thiols concentrated on the skins (similar to spent dry-hops). 

Because many of the free thiols from the Sauvignon Blanc grapes were released into the wine, the skins are still valuable because of the incredible number of thiol precursors, mainly the cys-3MH thiol precursor. Most bound thiol precursors in hops and wine grapes are glutathione-thiol (glut-thiol) and not cysteine-thiol (cys-thiol) conjugates. Bioegineered yeast strains can liberate bound cys-3MH precursors, which is why most of the research focuses on this class. However, hops and wine contain loads of glut-3MH precursors as well, and this post will get into how the potential of introducing glut-3MH precursors into the mash might help free even more 3MH. 

Look at Phantasm from inside the bag.

Reaching out to and collaborating with Jos Ruffell, the creator and founder of Phantasm (and co-founder of Garage Project in NZ), I learned a lot about how the powder is created, how it’s been used with other breweries, and what the future of the product might entail. 

Phantasm is a project that Jos has been working on for over three years. Living in New Zealand, which is known for its ultra tropical passion-fruit-like Sauvignon Blanc wines, Jos thought there might be potential for incorporating these thiol-rich wine grapes into beer. After all, one of the main thiols in these wines (3MH) is also key thiol brewers seek in hops. 

Utilizing only grape skins from New Zealand vineyards already known for their thiol-rich grapes, Phantasm powder would likely have a higher potential for thiol concentrations. Some vineyards have such incredible thiol-heavy grapes that “Thiol Bomb Tanks” are utilized to create highly tropical and passion fruit Sauvignon Blanc wines that can then be used to blend into wines that need the extra thiol-fruit boost. This is a process similar to breweries who keep extremely acidic low pH pale beer in tanks that they can use to increase the sourness in beers that didn’t quite get into the acidity range they were seeking.

This focus on using only high thiol blocks of grapes from winemakers is becoming increasingly crucial to the Phantasm process; the newest crop (2021) will include a known high thiol block, for example. To enhance the thiol potential even beyond terroir, Phantasm is improving its processing methods to concentrate the thiol and thiol precursors even more, potentially making a 3 g/L dose equivalent to an 8 g/L dose.

How much 3MH thiol potential are we talking about with Phantasm combined with a bioengineered yeast strain designed to bioconvert? While not every lot of Phantasm powder will contain the same amount of 3MH precursors (similar to how not every hop lot of the same variety will yield the same concentration of oils), you can still see the incredible potential in one tested trial at Omega Yeast. Although the average of ferments with Phantasm and Cosmic Punch™ was around 775 ppt of free thiols, the experiment charted below was on the higher end of the free 3MH average than a control wort with no Phantasm.  

Mash-Hopping

Now that we know that including the bound-thiol rich Phantasm powder in a beer (usually in the whirlpool along with thiolized yeast strain) can get you 3MH levels ~14 times above sensory thresholds let’s look at how utilizing specific hops in the mash might help to push these free 3MH levels even further!

The collaboration beer we brewed as the main topic of this post with Omega Yeast and Phantasm (named Locksmith) was inspired by the idea that the lock was the Phantasm powder, loaded up with cys-3MH precursors. The key was Omega’s new thioloized strain called Cosmic Punch™, designed to unlock the bound potential in hops and products like Phantasm. Not only did we want to include Phantasm in the whirlpool, but we piggybacked on some Omega trials deciding to go with Cascade as a significant mash-hop addition. 

Why consider mash-hopping? At least for grains, it’s the mashing process that releases the grain 3MH precursors into the wort. Cosmic Punch™, for example, is freeing 3MH precursors only from grain higher than most heavily dry-hopped IPAs. So on the surface, it makes some sense that it might also help hop-derived precursors get into the wort, but why? 

I reached out to Laurent Dagan, who has published outstanding research on bound thiol precursors. Dagan shared his thoughts on mash hopping potential by saying, “In malt, many enzymes are working during mashing; among these enzymes, there are many different peptidases. Thiol precursors we know are peptide derivatives (as glut-3MH). We can suppose (and it is true!) that these peptidases can change the balance between the different thiol precursors in the final wort, associated with a FAN change. All of which could change the release during fermentation.”

Dagan also shared that thiol precursors are highly polar, so the extraction of these cys and glut precursors is likely happening quickly on the hot side. Still, they haven’t done any studies yet to see what point in the process is best to add precursor-rich products (boil or whirlpool, for example). So, it seems that hop-derived precursors are making their way into wort when added to the kettle, but the mash might be where we can convert more of the glut precursors to cys, which is the class of precursors beta-lyase producing yeast can free. The more cys-3MH precursors we can push into the fermenter, the more potential for free 3MH! 

In addition, Laurent Dagan mentioned on an MBAA podcast that a protein rest might help with optimizing thiol conversion in some unpublished data they have formed. At lower temperatures in the mash (protein rest 113℉ or ~45℃), the enzymes are activated that transform bigger cys-3MH precursors into smaller precursors. Depending on the yeast, these smaller cys-3MH thiol precursors might be more readily released during fermentation. Or, perhaps more of the glutathione are converted to cysteine during a protein rest, whether that results in more free 3MH is still in question. Further, boiling wort will likely extract more of the thiol precursors into the wort, allowing a bioengineered strain to free them (not necessarily freeing them). So, we might conclude that using high bound thiol hops (like Saaz) early into the boil as a bittering charge may also help feed these precursors into the beer. 

Omega Yeast found increased levels of free 3MH in beers fermented with Cosmic Punch™ that had elevated levels of mash-hopping done, giving some evidence to this glut-to-cys precursor path. Omega maxed out their mash-hopping trials at rates close to 2 pounds per bbl (~7 g/L) with varieties known for their high bound 3MH potential (hops like Saaz, Calypso, and Cascade). 

Surprisingly, Omega saw even higher free 3MH in beers fermented with Cosmic Punch™ with significant mash-hop charges compared to equivalent rates of whirlpool charges! The mash-hops likely benefit from the high enzymatic environment of the mash, making these precursors more readily available (glut to cys) for the engineered yeast to free during the early days of fermentation. It’s also possible that less 3MH conversion with whirlpool hops vs. mash-hopping is due to stripping from high polyphenol vegetal hop material pulling out sensitive thiols (and precursors) during the whirlpool.

If you wonder what the IBU implications might be from mash hopping, Omega found that ~30% utilization in their trials of what you’d expect to get from the same amount of hops used as a 60-minute addition. In other words, you would get ~30% of the expected IBUs from a 60-minute hop addition with a mash-hop addition. Utilizing high bound 3MH hops with low alpha-acid content (like Saaz) is a great way to boost thiol precursors into the wort without worrying too much about IBU increases. 

As you can see from the chart above from Omega’s research, next to the control beer with a non-thiolized British V, Cosmic Punch™ ran away with the total free 3MH thiol count. In addition, in this case, with Chinook at 2 lbs./bbl (7 g/L) in the mash vs. added in the whirlpool, increased free 3MH thiols in the beer ~20% from the non-hopped sample (which just had cys-3MH precursors from the base grain). 

The surprising result above was how much lower the total free thiol content was with the whirlpool hop addition; in fact, the whirlpool beer had ~40% fewer thiols than the non-hopped control! Thiols resulting from mash-hopping would likely increase even more when using hops known to have even a higher concentration of bound cys/glut-3MH precursors. Laura Burns, Director of Research and Development at Omega Yeast, suggests the results would have likely been even higher for free 3MH when mash-hopping with higher bound thiols hop varieties than Chinook. Laura stated that in their many trials, “overall we have the biggest sensory bump with those hops known to have high precursor levels.” 

How is that whirlpool hops would result in fewer thiols? Isn’t that the whole point of whirlpool hopping, to push hop compounds into the fermenter? Should we stop whirlpool hopping? It seems that for the first question, it’s likely that thiols are sensitive enough to be pulled out in the presence of a lot of hop vegetal material. Although it’s just as much hop material in the mash in the current tests, it’s like the freeing or conversion from glut-3MH to cys-3MH that is pushing the thiol precursor count in the kettle (where they likely remain because they are so polar) and there is no big whirlpool addition then working to pull them out as the hops percolate through the kettle. 

Just in terms of sensory, we noticed a similar loss of perceived thiol concentrations after dry-hopping bioengineered Yeast beers during trials at Sapwood Cellars. In our experience, these strains did a seemingly great job releasing thiol precursors during fermentation, but after a heavy hit with dry-hops, the fermentation thiol character was significantly reduced. For example, in a test batch with Cosmic Punch™, comparing a sample post-fermentation and pre-dry-hop, the non-dry-hopped beer was super bright, with white grapefruit and exotic fruit aroma. However, after dry-hopping, the beer was pulled back into a more neutral and familiar IPA-like territory.  

One last thing regarding mash-hopping. At Sapwood, we have been utilizing mash-hopping for a while, entirely on separate research that suggests it may benefit shelf-life. As I wrote in The New IPA, alpha and beta acids from hops are good at complexing problematic metals released into the wort during mashing that can react with oxygen later on in the brewing process. For example, the paper cited found that early-stage hopping led to reduced metal concentrations (~30% fewer iron levels, for example) and improved oxidative stabilities compared to a reference beer. The higher the pH, the better the hop acids were at complexing the metals, so it might make sense then to add your mash hops before adjusting for mash pH to give the acids a complexing head start.¹

Potential Role of Hop-derived Heavy Metals

In conversations with Dr. John Paul Maye, Technical Director at Hopsteiner, upon visiting the brewery earlier this year, I asked his opinion on why this pull-back of perceived thiol flavor/aroma might be happening after dry-hopping. Although it needs to be tested, he thought it’s possible the vegetal material in dry hops themselves might be pulling out thiols as they fall through the beer (both in the kettle and fermenter). In addition, the heavy metals in hops may also be absorbing the sensitive thiols. For example, copper sulfate, sometimes used as a fungicide in Europe, can produce hops with little to no thiols. 

How much potential is there for metal pickup from hops? In a study of 15 commercial beers, those that were dry-hopped had the highest levels of metals. For example, an imperial IPA had 0.21 ppm of Manganese, and two different pale ales had 0.23 ppm and 0.15 ppm, compared to an American light lager with 0.05 ppm.[​​note] Porter, J., & Bamforth, C. (2016). NOTE: Manganese in Brewing Raw Materials, Disposition During the Brewing Process, and Impact on the Flavor Instability of Beer. Journal of the American Society of Brewing Chemists. doi:10.1094/asbcj-2016-2638-01[/note] Manganese, it appears from the study, is a metal from hops that is particularly good at extracting into beer (potentially then absorbing free thiols).

In the paper above, the longer the hops were in contact with the beer and the warmer the dry-hop temperature, the more metal pickup. Specifically, dry-hopping at 68°F (20°C) had 0.10 mg/L more manganese than the beer dry-hopped cold at 38°F (3°C), and manganese concentrations peaked after 5-7 days. It’s not just manganese in hops that could strip thiol (although it’s the most efficient at extracting into beer), as the paper found that iron and copper were also in beers after dry-hopping at high enough levels that could lead to oxidation problems. 

Along with other reasons, you may want to consider dry-hopping cool. This might help limit metal extraction from hops into your beer and potentially less thiol stripping (again, this theory would need to be tested).

Timing of Dry-Hop Additions and Thiol Losses 

The timing of the hop addition may also play a role when determining the potential for thiol-loss to vegetal hop material on the hot side of the process. The chart supplied below by Omega Yeast shows a higher total thiol concentration in beer when using fewer hops (.5 lbs/bbl vs. 2 lbs/bbl) when adding dry hops to beer on day one of fermentation. At least in this test, the additional amount of hop vegetal material may have helped to pull out or strip thiols. I wonder if the active fermentation (which would move around the hop material) might help pull out additional thiols, which is especially true when there is a greater amount of hops (2 lbs/bbl) in the beer. At least for this test, it appears that a little goes a long way for an increase in thiols with active fermentation dry-hopping when using a bioengineered yeast strain like Cosmic Punch™. 

On the flip side, 3MH levels increased without active fermentation on day 7 of fermentation when little, if any, CO2 production is likely taking place. However, as you’ll see later in the post with our samples for The Locksmith, we saw a reduction in 3MH with even a small dry-hop charge with the less vegetal material Cryo Hops® from Yakima Chief. 

So, the Omega Yeast test implies that there might be a benefit related to higher thiol concentrations with a small ½ lbs/bbl (~2 g/L) dry-hop during active fermentation (likely best during the first few days of fermentation). It’s important to take into consideration the impact of hop-creep with active fermentation dry-hopping. You don’t need to worry about off-flavors like diacetyl at this stage because the yeast cell rates are high and healthy. However, you might need to worry about subtle final gravity swings with active fermentation dry-hopping. The enzymes released into the wort from hops at this stage can work to free up dextrins and leave you with a dryer beer. It’s not a massive drop in gravity, but you could see a decline of ~.2 Plato. Another impact of active fermentation dry-hopping that Laura Burns mentioned is that it might also reduce the dissolved CO2 in the beer (by creating nucleation points), which can benefit yeast health as yeast don’t like CO2. 

Looking at our Locksmith recipe and going with the theory that hops may be pulling out thiols, we chose to go with a low dry-hop charge in the collaboration of only 22 pounds (in a 10 bbl batch) of Mosaic Cryo Hops® (usually we would dry-hop with 2x this amount in a DIPA). The logic is that a smaller charge could help reduce thiol losses, and Cryo, with less vegetal material (and likely fewer metal concentrations), might strip fewer released 3MH thiols. Lastly, choosing to dry-hop post-fermentation might also help prevent a loss of thiols as the Omega test saw much higher concentrations with the day 7 dry-hop vs. the early active fermentation charge. 

Oxygen and Thiols 

As mentioned at the start of this post, we wanted to take the collaboration of The Locksmith a step further in terms of analyzing the beer by sending samples to a lab called Nyseos in France to get tested for thiols (3MH, 3S4MP, and 4MMP). We were instructed to dose our sample cups with metabisulfite to help protect the thiols during transit. After adding the metabisulfite, we then froze the samples and shipped them to be analyzed via LC (not GC). Thiols, because of their low concentrations, are hard to test for and only a handful of labs even offer the service. The Nyseos lab uses very robust and controlled processes that allow them to quantify thiols accurately. 

I don’t want to go too far off-topic, but two things come to mind when learning that thiols are so sensitive to oxygen: 1) how important avoiding oxygen ingress is in beers chasing high thiol counts and 2) can beers with high total thiol concentrations potentially be more shelf-stable than low thiol beers due to their sensitivity to oxygen? 

Again, leaning on the knowledge and experience of Laura Burns at Omega, it was interesting to hear that in multiple samples they sent to Nyseos to get tested for thiols, those that were not treated with metabisulfite came back with samples all over the place. The frustrating results were likely the result of any oxygen ingress absorbing the thiols. 

Although additional research should be done in this area, it seems plausible that because thiols are so susceptible to oxygen, they may also be acting as one of the first waves of defense against oxygen (similar to sulfites). This can potentially mean that when using products like Phantasm and bioengineered yeast strains designed to free thiol precursors, you could be extending the hop-forward shelf-life in your beer. Because the thiol concentrations can be as high as +1,000 ppt (for free 3MH), even with some oxygen ingress and eventual thiol absorption, you could still be above the 3MH threshold and the total thiols taking the oxygen hit, not other important hop-forward compounds like free monoterpene alcohols or the eventual malt staling aldehydes (post-fermentation hop oils might also help reduce staling aldehydes).  

At least one academic paper we can look at for insight into thiols, oxygen, and shelf-life. The chart below shows the concentration of free 3MH in the beers studied during the natural aging of six top-fermented Belgian beers. As you can see, the thiols are almost entirely absent after one year and as quickly as six months in some samples. The reduction in thiols is likely due to their “high propensity to undergo oxidation, nucleophilic additions or substitutions.” The paper’s authors add that “antioxidant components (ascorbic acid, and sulfites) added either in the brewhouse or at bottling can help to preserve thiols.²

Source:Tran, T. T., Cibaka, M.-L. K., & Collin, S. (2015). Polyfunctional thiols in fresh and aged Belgian special beers: Fate of hop S-cysteine conjugates. Journal of the American Society of Brewing Chemists, 73(1), 61–70. https://doi.org/10.1094/asbcj-2015-0130-01

Interestingly, you can see from the chart pasted below, when lager beer was spiked with cys-3MH precursors, there was a conversion of the bound 3MH (cys-3MH) to free 3MH with time in the bottle. Although the conversion was relatively small (ranging from 0-19% conversion across the tests), you can see how increasing the thiol precursors in the beer could benefit its flavor longevity, especially when using a yeast strain designed to free those thiols. So, free thiols are likely to oxidize post-packaging (to a lesser extent if using metabisulfites), but thiol precursors can also continue to be released into a free state during aging.

Although the study here used a Belgian strain, I would guess that using a strain like Omega’s Cosmic Punch™ (or Berkeley’s Tropics strain) designed to free bound thiols with active beta-lyase activity would release substantially more thiols during aging. On top of that, the starting concentration of free thiols (especially if using high 3MH precursor hops or using Phantasm) would be incredibly higher. For example, Omega found free 3MH nearly twice as high as the beers tested in this study, and that was just from malt precursors (no hops). Although I would like to see a bioengineered strain tested for thiols throughout aging like in this study, if the majority of the Belgian beers had free 3MH above the threshold after two months in the bottle, the bioengineered strain would likely remain above the threshold for much longer at the same time potentially freeing addition bound 3MH during aging. All to say, I’m theorizing that using high thiol precursor products in combination with a strain like Cosmic Punch™ would result in a punchy aromatic beer with a more lasting flavor/aroma than a typical fermented IPA.

So, to sum up, the oxygen aspect of heavy thiol beers, it seems plausible that ignoring the sensory part altogether, high free thiol producing beers may act as the second wave of oxidation protection after the sulfites have been used up. Essentially, brewing high thiol beers, avoiding oxygen during dry-hopping and packaging, and even considering adding small amounts of metabisulfite at dry-hopping could all be ways of extending the fresh hop-forward shelf-life in IPAs. 

Role of Grains in Thiol Precersour Potential and Shelf-life Extension

When researching the book, The New IPA, it was interesting to learn that even protein-derived thiols from malts may serve a protective role in hazy beers, similar to how free thiols like 3MH might. Essentially, sulfites are the primary antioxidant in beer (produced naturally during fermentation or added post-fermentation via metabisulfite), and these protein-derived thiols and free hop thiols can act as a secondary antioxidant to encourage redox stability (oxidation). 

As it relates to malts, it’s challenging to know the total thiol content, but it has been found that the reduced and total thiol content in beer was highly correlated with total protein contents. However, it may not be as simple as just increasing total protein content, as not all proteins have the same antioxidant capabilities. 

To test out the antioxidative properties of the stable LTP1 protein (stable here means it is a protein that can withstand the brewing process better than other proteins), a paper experimented with three Australian lagers, one fresh off the production line (“fresh”), one aged for 12-weeks at 86ºF (30°C) (“aged”) and another for five years at 68ºF (20°C) (“vintage”). The authors found that the Australian lager characteristics remained in the fresh and vintage beers but were lost in the aged beer.³ The flavor stability of the fresh and vintage beers was then correlated with the presence of the LTP1 protein. Essentially, the authors concluded that the presence of thiol-rich LTP1 indicates that the protein can play a prominent role in maintaining the redox balance of beer from its free radical scavenging and antioxidant capacity in both fermentation and packaged beer.  Using the study results, you can make a case for enhancing LTP1 proteins in hazy, hoppy beers to try for flavor stability after packaging. 

Interestingly, the role of the LTP1 protein in promoting head retention may be partly because it’s rich in the same free thiols that might also play a role in beer stability. Structurally, the LTP1 protein consists of 8 cysteine residues, and this high content of thiol cysteine in the protein is likely the basis for its antioxidant effects. Similarly, with cysteine-bound thiols in hops (the thiol precursors), they too could act as an antioxidant when freed. 

So, to increase the protein-derived thiols to help with stability, we should be using grains high in the LTP1 protein. One possible way to do this is by brewing with a high percentage of under-modified grains (big fan of chit malt). ⁴

To speculate even further, I wonder too if malted grains that are under-modified (like chit malt) might be higher in the LTP1 protein (leading to potential higher shelf-life) and one of the higher cys-3MH precursor grains which a bioengineered strain can then act on and free. At least for The Locksmith beer, we brewed for this post (which included chit malt), it was one of the highest thiol beers tasted to date compared to various other beers Omega has tested. 

Laurent Dagan continues to research malt and thiol precursors, and I look forward to reading his results. So far, they have done experiments testing 15 different malts, and the barley malts were all higher than non-barley (rice, sorghum, and wheat). As you can see from the chart presented in an online presentation from Dagan below, not all barley malts are equal precursor potential. It seems that less a grain lightly kilned malts help to retain these precursors.

Source:https://www.youtube.com/watch?v=Ob5Jxy2cKLs

In an October 2021 MBAA podcast, Laura Burns described that in various ferments they have done at Omega yeast, the grain with the most sensory impact of freed thiols with their Cosmic Punch™ strain has been a local wind-malt variety. Specifically, the wind-malt was with a local roaster in Indiana that produces the malt by avoiding kilning altogether as it’s dried in the sun instead. So wind-malts might be a good base malt to experiment with when using these beta-lyase-producing yeast strains. Mecca Grade Estate Malt in Oregon is one of the few wind-malts I’ve seen for sale. In general, though, Laura explained that barley malts were still “bringing a lot of precursor in,” and they have also found (not sure why), but when “wheat is in the beer beyond 20%, you start to lose the thiol impact.” This could potentially be that malted wheat just doesn’t have as much precursor thiol potential, which is what was found in the one variety in Dagan’s tests above, along with rice and sorghum malts.

Understanding Thiol Precersour Potential 

Because thoil precursors can come from multiple sources (hops, fruits, and grains), it seems helpful to look at the potential from each source. Again, remember that a yeast strain that is capable of producing the enzyme beta-lyase during fermentation is needed to free the precursors to allow them to have a sensory impact on the beer. 

Grain

When it comes to grain, there is still room for experimentation to understand what is increasing precursor counts, but the chart below from Omega Yeast (in Cosmic Punch™ ferments) shows the potential from just a 2-row base malt. With the thiolized Cosmic Punch™ strain (and no hops at all), the cys-3MH precursors in malt were enough to get the beer way above the free 3MH threshold of 60 ng/L getting to 546 ng/L. This is compared to a ferment with the same parent strain of OYL-011, which produced only 11 ng/L of free 3MH. It would be interesting to see the same test done with thiol-rich lightly kilned LTP1 grains included in the grist. 

Amount of thiols released from malt precursors (data supplied by Omega Yeast)

Phantasm

Although each batch of Phantasm might vary in its total cys-3MH precursor concentration, the results tested so far show that using the dried Sauvignon Blanc product with a beta-lyase producing yeast will get you at extremely high free 3MH levels. In smaller flask fermentation trials, Omega found that compared to a control wort with no Phantasm, across four ferments, the Phantasm beers averaged an increase of 441 ppt or over 130% increase in free 3MH! The highest precursor lot of Phantasm increased the free 3MH thiols 583 ppt (over 170%). It’s obvious now why we wanted to call our collaboration beer The Locksmith when you see the potential of a bioengineered yeast strained designed to unlock bound thiols and a product like Phantasm loaded with bound potential. 

Hops

Again, not all hops are the same for thiol precursor potential, but for the hops that have been tested to date in the literature, below is a chart of the potential in 17 different hops. I hope the cys-3MH (and glut-3MH) figures are something that hop suppliers consider testing and advertising along with their hop oil information as our understanding of the potential in bound compounds continues to improve. Having this type of information can help us understand when and how to use certain varieties.

It’s probably important to remember that because the freeing of the bound thiols is happening inside the bioengineered yeast cell itself, it’s probably best to try and load your wort with precursors (from malt, hops, and products like Phantasm) prior or during the start of fermentation or you might miss the window for freeing 3MH. That’s not to say that releasing thiol precursors won’t happen post-primary fermentation, as the Belgian study above found, or as was the case in late dry-hopping in the Omega trials. I would assume this continual freeing would be significantly halted when the beer is stored cold, however. This also brings up the idea of using bioengineered strains to re-ferment and condition beers that might have high thiol precursors when bottling beer (mix-fermentation wine grape beers or dry-hopped sour beers, for example).

The Locksmith Recipe and Results

Collaboration with Omega Yeast and Phantasm

To help us better understand how big the Phantasm’s role powder might play in this batch, I pulled ~17-gallons before the whirlpool Phantasm addition to fill a smaller half bbl Spike conical fermenter. A week into fermentation, we pulled some samples before dry-hopping to see how the Phantasm beer compared to the non-Phantasm ferment. It was highly evident that the precursors from the Phantasm impacted the beer’s sensory. The bigger batch ferment (10 bbls) was white-wine forward, with a touch of Welch’s-like white grapefruit juice, whereas the non-Phantasm beer was relatively neutral. 

In general, when comparing our smaller trials fermented with Cosmic Punch to our RVA Manchester ferments, the Cosmic Punch beers (pre-dry-hop) tended to be brighter and less doughy/malty. This quality (likely from simply having more intense fruit-forward thiols released) is a nice base for dry-hopping. Although we found that dry-hopping these bioengineered strain beers can greatly impact the sensory of the thiol-ferment, whether this is by hop vegetal material stripping or hop metals absorption, or masking, the brighter, less worthy base seems to allow the dry-hops to pop more with less malt competition. 

Again, we used Mosaic Incognito to get some bitterness without introducing lots of vegetal material that might strip thiols. Likewise, we did a small (2.2 pounds/bbl dry-hop (8 grams/liter) to get some dry-hop character again but hopefully with less pullback of thiols with the smaller charge in combination with less vegetal material in Cryo. As you can see in the chart below from our tested results, The Locksmith did see a decrease in thiols after even a small dry-hopping charge with Mosaic Cryo, especially with the passion-fruit forward 3MHA thiol. I suspect the thiol levels would have decreased even further with a bigger dry-hop charge (5+pounds/bbl), especially with T-90 pellets, as more vegetal material might pull out additional free thiols.

Sensory, you could taste this pullback, despite the thiols still well in and above their respective threshold limits in beer. I’m sure it’s partly the slight reduction from the dry-hop, but there is likely some type of free-thiol masking taking place with all the other compounds dry-hopping brings to the beer (polyphenols, hydrocarbons, terpenes, etc.). For the Locksmith, after dry-hopping, I didn’t have nearly that grapefruit juice-like taste we were getting before the dry-hop. However, the beer maintained the brightness that Cosmic Punch™ brings.

The beer has a nice fruitiness that we typically wouldn’t get with just a Mosaic dry-hop with a non-thiolized London Ale II. Overall, the beer had low sensory bitterness and finished just a touch too sweet. The combination of the two wasn’t my favorite; I think we should have tried to dry the beer out a touch more and bring a little bit more from the hot-side hopping (perhaps more Incognito). The overall hop flavor of the beer is relatively weak, but that’s to be expected with such a small dry-hopping charge. It misses that DIPA-like hop intensity that people would expect in a beer like this. However, the lower Cryo rate kept a bit more of the thiol-fruit aromatics produced during fermentation, especially when considering other trials we did that were dry-hopped much more heavily.

The Locksmith was a unique DIPA; I’m not sure I’ve ever tasted something in this type of category of IPA before. I liked it a lot! However, being sold as a DIPA, I think we’d have to up the dry-hopping, which would ultimately reduce that fermentation character we like. There may be potential in post-fermentation hop oils to go along with a smaller hop charge in beers like this to get them up to that DIPA hop-like level without introducing too much hop vegetal material.

The other interesting thing we found in this beer was the pH change brought from the Phantasm powder and the Cryo dry-hop. Post-boil (with a 5.18 mash pH), the Phantasm dropped the whirlpool pH to a low 4.78. We typically add phosphoric acid to our kettle to lower the pH to limit color pickup from Maillard reactions but didn’t in this beer because of the pH drop from Phantasm. The result was a beer with more color than we were going for. Perhaps we could have added some Phantasm as we filled the kettle to get us where we wanted to be. Because thiol precursors are so polar, they would have likely remained in the beer throughout the boil. We could have also considered adding baking soda to the whirlpool to help offset the pH drop that Phantasm brings.

As for The Locksmith’s pH, it was only 4.16 pH before dry-hopping and rose only slightly to 4.21 after the Cryo dry-hop. The slight increase is because as the vegetal material increases in the dry-hop, so too does the pH of the beer. This lower pH, much lower than most of our IPAs, also contributed to a not a DIPA vibe. Just something else to consider when experimenting with Phantasm!

Phantasm Without Beta-Lyase

I was curious how Phantasm powder might work when using it with a yeast strain not bioengineered to unlock bound 3MH thiols, so I reached out to Mike Foniok, head brewer and owner of The Establishment Brewing Company in Calgary (as they are not allowed to use these yeasts yet Canada). Mike has one of the highest-rated Phantasm beers on Untappd with a hazy DIPA called Irrational Things, so he seemed like a good person to ask!

Irrational Things (8.5% DIPA)
Malt: 2 Row, Flaked Oats, Flaked Wheat, Malted Wheat, and Chit Malt
Hops: Galaxy, Equanot, Azacca, Citra Incognito, and Mosaic Cryo
Yeast: Escarpment Labs Foggy London

The establishment utilized Phantasm in the beer by loading it in the whirlpool and then followed that up with a smaller active fermentation addition. The whirlpool addition was 1.3 lbs./bbl (5g/L) and the fermentation addition was ~0.5 lbs./bbl (1.8g/L). They didn’t want to displace the number of hops that they usually put into the whirlpool with phantasm powder; instead, they wanted it to be in addition to their regular whirlpool hopping as an additional layer of potential flavor. Since their whirlpool vessel limits how much matter they can physically put in it, they relied on Cryo Hops® and a small addition of incognito in the whirlpool (which may have preserved some thiols via less hop vegetal material).

In terms of the aroma impact from the Phantasm in the whirlpool and during primary fermentation, Foniok noticed that the hop aroma impact in the beer pre-dry hop addition was more intense than usual in sensory when considering their whirlpool hop load was very similar to a typical Imperial NEIPA. Like with some of Sapwood’s trials with Phantasm, The Establishment saw pH drops in the whirlpool compared to their conventional whirlpool hopping methods. Below you can see the pH reduction in three consecutive batches of the beer with Phantasm added to the whirlpool. Essentially, they averaged a ~0.30 ph drop when using Phantasm at a whirlpool rate of 1.3 lbs./bbl (5g/L).

In terms of shelf-stability impact from thiols coming from the Phantasm powder, Foniok anecdotally thought this was the case. They didn’t do a warm vs. cold-stored double-blind to confirm these observations, but the beer’s hop aroma and the flavor did seem to stay at “its peak” longer than typical. In terms of dry hop matter pulling out any free 3MH thiols that may have been present on the dried wineskins, they didn’t notice as much of a pull-back as we did in some of our trials. I would assume this is partly because the number of free thiols was so much less post-fermentation using a conventional yeast strain.

Conclusion

To try and bring all this information together into some type of visual, below is a chart of many of the different thiol tests discussed in the post. Below the chart is the usual key points summary I like to include in posts of this length. You can see how the different potential in unlocking bound thiols compares with other products (grain precursors, mash hops, whirlpool hops, and phantasm) compared to a control. Using the science available at the time of writing for The Locksmith, we tried our best to formulate a recipe that might help push thiols as much as possible; luckily, we achieved that goal!

Cheers!

Scott

Key Findings 

• Hops have both free and bound thiols. Hops that are high in free thiols (like Citra and Simcoe, both high in 4MMP) are more efficiently utilized as a dry-hop. Hops high in bound thiols (like Saaz and Calypso, both in cys-3MH) are more efficiently used early in the process, especially when paired with a bioengineered yeast strain designed to free the bound thiols (mainly cys-3MH).

• Yeast strains bioengineered to unlock bound thiols have the necessary gene (IRC7 for Omega yeast) or TnaA (for Berkeley yeast) to produce the required enzyme (beta-lyase) during fermentation to unlock thiols (going from cys-3MH to free 3MH). Not only are the genes inserted, but they are overexpressed, which means the gene activity is turned up or highly expressed, allowing for an even greater release of bound thiols.

   

• Phantasm is an extract of New Zealand Sauvignon Blanc grape skins (targeted for thiol-rich grapes) processed into a powder that, like hops, are high in thiols and thiol precursors (cys-3MH). Specifically, an average of Phantasm ferments with Cosmic Punch™ yeast had ~450 ppt more free 3MH than those with only grain.

   

• Mash-hopping as high as ~2 lbs./bbl (7 g/L) with high bound 3MH hops (like Saaz, Calypso, and Cascade) can increase free 3MH concentrations (even higher than whirlpool hopping).

   

• In terms of bitterness from heavy mash-hopping, Omega found ~30% utilization in their trials of what you’d expect to get from the same amount of hops used as a 60-minute addition.

   

• Free thiols can be pulled out and masked by heavy dry-hopping rates. Utilizing less vegetal material products like LUPOMAX™ and Cryo Hops® or post-fermentation hop oils might be ways to increase hop flavor while maintaining more free thiols.

   

• Active fermentation dry-hopping might also act to pull out free thiols compared to post-fermentation hopping. If an active fermentation dry-hop charge is wanted, a smaller dosage has been shown to increase free 3MH thiols than more significant charges.

   

• Free thiols are very sensitive to oxygen, so avoiding oxygen during dry-hopping, purging vessels/bottles/cans, and even considering the use of metabisulfite might be a way to preserve thiols freed during fermentation and dry-hopping.

   

• Thiols (especially in the presence of yeast strains capable of beta-lyase activity) can continue to unlock precursors during storage, suggesting they may be great bottling strains if using high bound thiol products as part of the recipe.

   

• Grains themselves can contain 3MH precursors, especially those lightly kilned or not kilned at all (wind malt may be exceptionally high). In one test, malted wheat was a very low source of 3MH precursors. Bioengineered yeast strains designed to unlock these thiols are essential to achieving high free 3MH, however.

Exploration of Post-Fermentation Hop Oils

Overview and Results of the Different Hop-variety Specific Oils

When new hop products hit the market, they are usually viewed with equal amount of excitement and confusion. Post-fermentation hop oils fall into this excitement confusion category for me. Are they supposed to replace dry-hopping all together? Are they just for the bigger breweries concerned with maximizing yields? How do you even get the oils to mix in beer evenly? Are they just for flavor and aroma or do they have other implications like mouthfeel and bitterness changes? These are the types of questions I’ll try to answer in this post.  Attempting to research hop extracts and how they perform in beer was surprisingly challenging; most of the papers I could find focused more on the bittering capabilities of such hop products rather than flavor implications. Relying heavily on a few of the most recent papers on hop oils, interviews with the hop oil suppliers and academic authors on related studies, and my own personal experience, this article is hopefully a helpful starting point for brewers to start thinking about their own experiments with post-fermentation oil dosing!

Why Even Consider Hop Oils? 

First of all, why even consider hop oils? One small but helpful reason to consider using hop extracts is the ability to store them in a small bottle at ambient temperatures for up to a year. At Sapwood Cellars, our cold room is stocked full of cans, boxes of pellets, and kegs. Another obvious benefit to brewers is increasing the yield of actual drinkable beer! I was much less concerned about this as a homebrewer, but getting a full 5-gallons (19-liters) out of an extremely hoppy beer is a nice perk. Essentially, efficiency is raised by using highly concentrated oils and less hops to lower the amount of hop material going into the kettle or fermenter and soaking up beer.

Another perk to hop oils focused on flavor and aroma is their ability to be used post-fermentation without causing any potential for hop-creep. Hop creep, for those unfamiliar, is essentially the ability of enzymes in hops themselves that can free up unfermentable sugars (dextrins), which can lead to re-fermentation. This re-fermentation can occur in an environment where little yeast is present (when dropping the cone for example), leading to off-flavors like diacetyl. All of the hop oils mentioned in this article have denatured these hop-creep inducing enzymes, allowing for pre-packaged use without fear of further re-fermentation.

Manufacturers of oils will often say that using post-fermentation oils can also help the shelf life of hop-forward beers. I always assumed that the presence of higher oils might mask or alter staling characteristics, but a 2011 paper dove a little deeper into stability. Specifically, the authors measured the staling aldehydes (bound aldehydes might be released over time, causing stale aged flavors) in the beers with and without oils. They found that beers with the hop oil essence had a generally lower concentration compared to those without. ¹ The authors would not go as far as to say the hop oils have some sort of flavor stabilization mechanism, but it should be studied further.

But, beyond some practical reasons to experiment with hop extracts, I think the most critical question is whether they help make better beer? Increased yields are excellent; better extraction of oils into the kettle is also great, and not worrying about hop-creep is a perk. But, unless these are actually improving the beer quality (or at the very least maintaining the same quality while using fewer hops), I’m not sure I’d even consider using them!

Potential Concerns with Post-fermentation Hop Extracts

One of the issues with hop extracts is that they need to be emulsified to mix evenly into beer. On their own, hop oils, when added to beer, would likely float to the surface. Because of this, a carrying agent is needed to mix with the oils to make them soluble in the beer. Two of these common carriers are propylene glycol (1:100) or ethanol (1:10). For example, if you want to add a total of 5ppm of pure hop oil to your beer you would also be adding ~100 times that amount (500 ppm) of propylene glycol, which is still a very small percentage when you take into account your batch size. 

Propylene glycol strikes me as an ingredient I’d prefer to keep out of beer. Still, it is widely used and approved by the FDA as a preservative and solvent in pharmaceuticals, saying it is “generally regarded as safe.” ¹

Aside from the use of a carrier like glycol or ethanol (like Everclear) being used, there are factors to consider with oils like what hop-derived oils are being extracted because of their new soluble state (which can differ from straight up dry-hopping). In a discussion with Spencer Tielkemeier, East Division Lead and Brewing Innovations at Yakima Chief Hops, Spencer expressed this potential concern when I reached out to see if they had any extract products on the market.

Spencer’s main concern is that “the use of an emulsifier typically means that, by making the oil-soluble, you typically make EVERYTHING soluble. This means that oil fractions that would normally be gassed off or removed during a typical brewing process (i.e. hydrocarbons like myrcene and caryophyllene) are now fully soluble and present themselves in the finished product.”

“The end result is often a beer that shows interesting hop aroma, but is absolutely dominated by less pleasant woody and vegetal aromas from the hydrocarbons. Most other desirable aromas are masked by the sheer quantity of hydrocarbons. Beers produced in this manner often taste similar to chewing on a raw hop pellet. Interesting, but not exactly pleasant.”

Yakima Chief has experimented with creating a post-fermentation hop variety-specific oil extract from hop extract but has yet to release anything because their trials are exactly what Spencer was alluding to, hydrocarbon dominate beers with less than ideal carries for emulsifying. For now, their best product for late hop punch is their line of Cryo Hops®. To help explain some of Tielkemeier’s concerns with oils, the best place to start is comparing what is actually extracted when dry-hopping compared to using an emulsified oil.  

What’s Extracting During a Dry-Hop?

For me to start thinking about hop oils and how they might differ from dry-hopping, I thought it was best to start with a paper from 2019 authored by Thomas Shellhammer and Dean Hauser at Oregon State University. In the paper, the authors dry-hopped at a rate of 1 pound per barrel with whole-cone hop varieties Amarillo, Cascade, and Centennial in a 24 hour dry-hop. First, the hops themselves were tested for total oil potential. After, the beer was tested for actual oil compounds extracted during the dry-hop. Finally, the spent hop material was tested again to see how much of the original hop oil potential still remained. The paper is great because it shows how inefficient dry-hopping can be in terms of oil extraction, something I think you’ll see is a major difference than using oils.

The graph of the results below is super interesting as you see how little of some of the hydrocarbons (some of the most volatile, green, resinous, and woody compounds) are making it into the beer during a dry-hop, despite taking up so much of the hop oils total oil percentage. In addition, the second chart listed makes it clear how many oils are wasted when dry-hopping with such a large percentage still residing in the spent dry-hops. As the paper’s authors conclude, “the results of this investigation provide proof that dry-hopping is a relatively inefficient process, and that spent dry hops waste on both a pilot and industrial-scale contain a considerable quantity of both volatile and non-volatile hop constituents.”

A great example above is with the hydrocarbon myrcene, the hops tested ranged from 371 to 2,382 mg/100g, by far one of the most significant portions of the hops total oils. Despite representing so much of the hop, only 14-25 ug/L of myrcene was tested in the final beers, with an amazing amount (258-2,163 mg/100g) remaining in the spent hops! In other words, only about 0.05% of the available myrcene from the hops are making it into the beer during the dry-hop. Although myrcene has recently been found to reside in hazy NEIPA’s at higher rates (as you’ll see below) you can see why dry-hopping with a variety like Citra, which is super high in myrcene, doesn’t give you an incredibly resinous and green result because so much of this compound isn’t finding it’s way into beer.

Just to help give you an example of how much myrcene is actually extracted into hazy beers on the commercial level (which is more than other styles, likely due to its viscosity) the chart below from Hopsteiner via Dr. John Paul Maye shows that in the hazy commercial IPAs tested, the maximum found was close to 2.5 ppm. ¹Hidden secrets of the new england ipa. (2018). Technical Quarterly. “>https://doi.org/10.1094/tq-55-4-1218-01[/note] Keep in mind, this is considered to be a relatively high amount across beer styles.

You are probably fairly wondering why I’m so concerned with myrcene levels with dry-hopped beers. The answer falls into how drastically different hop oils are in their creation and extraction percentages. Some of the oils available claim a nearly 100% of the already emulsified oils could get into the beer when used post-fermentation. Hopsteiner suggests in their technical sheet on their oils, for example, that the recovery rate for certain aroma compounds can be as high as 95%, remember that the test above for only 0.05% of myrcene being retained!

To put this concept of oils vs pellets into a real-world application, consider dry-hopping with Citra which can be as high as 70% myrcene compared to using a Citra post-fermentation oil extract as many of these oils are now created from hop-specific varieties. If the ~70% of myrcene from Citra is extracting and staying in the beer from an oil extract, I would theorize that the result would be a complete resinous and green bomb of a beer that would be nearly impossible to achieve based on previous research with hop pellets alone.

Now, I don’t want to brag, but I sent a beer into Hopsteiner for Dr. John Paul Maye to test it for various compounds (results pictured below), including myrcene. I had over 2.5 times more myrcene than the highest commercial beer tested in Maye’s study for this particular beer. The beer that was tested was one that had zero hot-side hopping done but was hit with an ounce of hops during fermentation and another 8 ounces of dry-hops (split between Citra and Amarillo) late and post-fermentation (for a 5-gallon (19L) test batch). I theorize that the lack of hot-side hopping allows for greater retention of hydrocarbons like myrcene with big dry-hop loads. The result of which, in my opinion, is not a very good beer that comes across as very vegetal and one-note. I bring this particular beer up just to show that a super myrcene-heavy beer with dry-hops alone wasn’t very good with too much resinous vegetal notes in my opinion and oils could theoretically achieve even higher rates.

Nothing is wrong in my opinion with myrcene per se, I think a certain amount of it can help to give that fresh green out of the bag dry-hop experience. However, when getting such high extraction efficiency with oils (or even in my case with no hot-side hopping and heavy dry-hopping) it seems logical that the oils would put these myrcene levels (to stay with the example) at rates never really seen in beers before. This is particularly troubling as one paper found that myrcene at even low levels resulted in metallic and geranium-like aroma notes concentrations at just 0.86 ppm. ¹

Solubility Maximums

Is it even possible for 100% of an oil extract and all the compounds residing in it (like myrcene) to extract into the beer? In a conversation with Thomas Shellhammer and Dean Hauser, who authored the paper above on dry-hopping efficiency, they explained to me that this isn’t likely the case. Solubility maximum is a concept where if something is already saturated to the max, adding more won’t reside in any more of that particular compound into the liquid phase because it simply can’t get into solution anymore. It’s kind of like if you jump into a lake with all of your clothes on, jumping in a second and third time won’t get you any wetter!

To give you an example of how far away dry-hopping alone is getting you to maximum thresholds, consider the following results from the OSU study discussed above (done at 1 pound per bbl). The linalool found in the test beers ranged from .08-0.281 ppm, nowhere near the max solubility of ~1,500 ppm. The same for myrcene, where the test beers ranged from 0.014-0.025 ppm, again, nowhere near their maximum ranges of ~10 ppm.

Although to date, no testing that I’m aware of has looked at using post-fermentation hop variety specific oils and measured dosed beer before and after to see the exact extraction efficiency rates. Hopefully, we can get this tested in the future to see if using oils gets us closer to the solubility maximum for some of the essential oil compounds. The question of if we even want to be near these maximums is a good one. But even just getting a better sense of the oil potential in post-fermentation oils to the resulting amounts in the actual beer would be super helpful as these products advance.

If there is a solubility maximum when dosing oils, should we even be worried about overdosing? It makes sense to me that if you can’t even get certain oils into the beer over certain limits, you theoretically could just pump in the oils until they are saturated and the non-saturated just kind of disappear? That’s probably not the case either, says Shellhamer. There still could be an impact of dosing oils over their limits despite not being the liquid phase of the beer. For example, you’d probably taste these extra compounds when they warm in your mouth. Despite not being in the beer, they are still there to some degree, likely on the surface.

In different benchtop dosing trials at Sapwood with varying amounts of certain post-fermentation oils to beer, I suspect some of these non-solubilized oil flavors impacted the samples. When we went too high with the dosing rate, we could taste strong extracty-like flavors. It would be interesting to see if the compounds were at or near their respective solubility maximum. Still, it was clear that too many of these oils started to lose variety-specific flavors, and the beer would taste generically green and herbal. In other words, the higher the dosage rate, the more the beer would taste the way the extract smelled out of the container.

Analyzing the Sensory Experience of the Different Hop Oil Classes in Extracts

Before diving into the different hop oil extracts on the market and some of our experiences with them, it’s interesting to look at a 2021 paper that examined how the individual sets or fractions of hop oils can impact beer. For help with a visual on the different hop classes and how the generally represent the total oils in hops, below is a chart I had made when writing The New IPA, which helps to reference as the results of this study are described.  

Keeping in mind the different classes of oils in the chart above, the work done in the Journal of the Institute of Brewing really helps to illustrate how greater extraction of certain classes over others in hops oils may have big impact on the overall flavors and mouthfeel impacts in the beer. The authors used Magnum hop oil and analyzed the specific fractions of oils in a pale lager beer. The fractions of oils separated out and tested by a sensory panel included sesquiterpenes, terpene alcohols, humulene epoxides, and monoterpene alcohols sesquiterpene alcohols, humulol +, humulenol II, linalool, geraniol, and caryophyllene oxide. ¹ They didn’t test a Magnum hop extract as a whole (all of the oils together). Instead, they fractioned off the oils and did a sensory tests individually. This type of examination is helpful because it can show how a greater extraction of some the fractions (like hydrocarbons) when dosing with oils vs. dry-hopping might impact the beer.

When it came to overall aroma and flavor intensity, the geraniol and terpene alcohol fraction scored the highest, and the caryophyllene oxide and humulene epoxides fractions were the lowest. Likely, the higher scores for geraniol and terpene alcohol fraction could be because of their respective flavor thresholds and the more polar nature, allowing them volatile less than other compounds. The geraniol and terpene alcohol fraction also increased the perceived sweetness intensity in the beers.

The panel found this sweeter and fruity fraction associated with descriptors as lemon, pinewood, soapy, rose water, orange fruit, and grapefruit. Interestingly, linalool (which is often a marker for “hoppiness”) was not found to be strongly characterized by and particular flavor or aroma term, and it’s likely more of a flavor enhancer as it relates to dosage via hop oils. Also interesting was that the malt character of the lager beer was not found to be impacted much by adding the various fractions of oils.

As it relates to bitterness perception, the authors found that the sesquiterpene fraction flavored beer had the highest scores for “harsh bitterness.” Whereas the beer spike with the geraniol fraction had the highest scores for “smooth bitterness.” Specific compounds that were found to increase harshness were a-humulene, δ-cadinene, β-caryophyllene, β-myrcene, and caryophyllene oxide, and the combination of compounds could drive the bitterness sensation.

As it relates to astringency (a common issue in some hazy IPAs), the highest oil fraction was the humulene epoxide beer. The results aren’t entirely surprising, considering that humulene epoxide is part of the spicy sesquiterpenoid fraction of hops.

An email exchange with Christina Dietz, an author on the paper in discussion (also part of her Ph.D. project), helped give some further insight into their sensory results of the Magnum hop oil. For example, regarding the greener hydrocarbons masking fruitier flavors, Dietz shared that this may be true for some extracts (of specific hop varieties) but others, these fruitier compounds can be in concentrations too low to be noticed, rather than being masked. This suggests that the hop variety used can make a difference as the fruitier the pellet, the likely fruitier the oil. But indeed, their results did find that “other compounds inducing “green” flavors (musty, earthy, woody, grassy) were found to be involved in harsh, bitter notes and astringency.”

However, Dietz explained that just because some of their results pointed to certain oil classes being more bitter and having certain mouthfeel implications, this should not necessarily be seen as a full-scale bad thing. The “harsh bitterness and mouthfeel characters would certainly fit with other beer styles.”

I asked Dietz about her thoughts surrounding potential solubility maximums with hop oils dosed post-fermentation. According to their tests, using calculations, they can confirm that the hop oil fractions did not 100% solubilize into the beer. Dietz explained that “whether a hop extract is 100% or near 100% soluble highly depends on the polarity of the matrix and the polarity of the hop oil compounds.” This logic makes sense to me, especially when thinking about hazy IPAs and post-fermentation oils. I would guess that the more viscous nature of the hazy IPA would enhance the retention of some of these otherwise volatile compounds (like myrcene as found by Maye above) and still push them way past what you would get when dry-hopping with pellets alone.

It’s interesting to consider the different sensory thresholds when you take into account the matrix to which the compounds are being tested. In other words, it would make sense that dosing a post-fermentation hop oil into water at the same rate as dosing into a hazy IPA would yield different results. Dietz explained to me that different sensory approaches and variables involved in the testing could impact results like the different types or styles of beer the oil is tested in, other tasting protocols, panel sizes, and statistical analysis approaches. Even the definition of “sensory threshold” can impact results (orthonasal, retronasal, detection threshold, recongition threshold, etc.).

I like to mention Dietz comments on the complications of different tasting matrixes because even in our small trials with the various oils at Sapwood, we got completely different results when dosing in an unhopped lager vs. a heavily dry-hopped NEIPA, for example. To me, the lager with the oil, although subtle, didn’t add to the beer but instead stood out in more of an artificial way. In contrast, oils dosed in the beer named Full Measure (described below) added to the complexity already in the beer to help complement and amplify what was already there.

I appreciate the work done by Dietz and her colleagues, in part, because it gives a great baseline of how these different oil classes might impact a beer and helps to think about how to alter some of these oils to make them fit certain situations or beer styles better than others.

For those that tend to be more of a visual learner, below is an interactive chart I created to help explain the results of the study above showing which hop compound classes had what type of sensory impact on the test beers.

Totally Natural Solutions

Finally, lets talk about some actual hop products with some results! I’m starting here with Totally Natural Solutions (TNS) because in terms of the different oil extract products out there, TNS has the unique ability through their proprietary processes to alter the concentrations of these different hop compound classes. Essentially, their oils undergo the same steam distillation process to isolate hop oils, but at this point using their patented fractionation to fine-tune the total oil makeup. In other words, this fractionation technology allows them to alter individual classes of oils, allowing for true-to-type hop variety character (raising/lowering the specific oils to more closely resemble the hop itself). Or, another potential use is they could potentially back down entire fractions (like sesquiterpenes), allowing compounds like monoterpene alcohols to potentially sing more by not having to compete with strong green flavors. Essentially, think about the paper discussed above looking at which classes of oils impact a beer in certain ways and then reducing or eliminating some of those classes to achieve potentially better results.

Totally Natural Solutions likes this combination approach to creating their oils because it’s a solvent-free way to mimic varieties at different parts in the brewing process. Suppose you have the ability to lower hydrocarbons like myrcene using fractionation technology. In that case, you could potentially more closely resemble using a hop during the whirlpool where a large percentage of myrcene would otherwise be removed due to steam in the kettle, trub, and active fermentation (this is the idea behind their HopShot® line of oils whereas their HopBurst® line isn’t fractionlized). Depending on how this actually translates into beer, it sounds exciting to give brewers a targeted method for amping up their beers post-fermentation if they lack hop saturated flavor or if the dry-hop was more lackluster than anticipated.

If the terminology of these oil fractions sounds familiar from earlier in this post, it’s likely because two of the authors of the paper have ties to Totally Natural Solutions. Pedro Oliveria is the technical Director, and Colin Wilson is the Managing Director of TNS. It makes total sense to me that a company with the capability of adjusting entire hop fractions from a steam-distilled extract might be curious how these hop fractions are realized on the palate. For example, if sesquiterpenes are responsible for some negative aspects of oil use, like increased bitterness and musty, earthy flavors, why not lower this fraction to make the hop oil more approachable?

In collaboration with New Zealand Hops and Totally Natural Solutions we brewed up another beer at Sapwood, trying to work on a larger scale some of what we learned in smaller experiments. For the beer that was eventually called Full Measure, we went full-on Nelson Sauvin! We mash hopped with .2 pounds per bbl (1 g/L) of Nelson Sauvin, followed that up with 2.2 pounds per bbl (~8.5 g/L) of Nelson Sauvin in a 180°F (82°C) whirlpool, and finally double-dry-hopped it with 3.3 pounds per barrel (12.5 g/L) of Nelson Sauvin post-fermentation. Finally, we then did benchtop trials dosing Nelson Sauvin oils from TNS into individual glasses to ultimately dose 10 grams/hL of Nelson Sauvin (called Victory) HotShot® and 10 grams/hL of Nelson Sauvin HopBurst® made it into the beer. 

The result was one of the punchier pale ales we’ve ever brewed, it didn’t hurt that the Nelson smelled great from the start. Here’s what the Untappd drinkers had to say regarding Full Measure. It was interesting when dosing the beer in smaller trials, going above that 10 grams/hL of the HopBurst® (which isn’t fractionalized) really started to increase the bitterness perception and start to get “extracty.” The Fractionalized HopShot® was much tamer and I liked the overall brightness it brought to the beer without too much of the green-leaning characteristics. 

In a collaboration between Other Half Brewing and Sapwood, we asked TNS if they could make us a custom oil after getting a chance to work with their Nelson Sauvin options. Using the same logic explained so far in the post, the ask of TNS was to use their fractionalization technology to create an oil 100% from Simcoe hops (which is called Geronimo from the HopBurst® line) as the reference hop profile. From here, TNS “fractionate heads/tails and optimize the oil to spike fruity fractions”. The hopeful result is a lighter lower myrcene impact type of profile that will tend to be closer to what both breweries were looking for from the oil. Essentially, we wanted more of a saturated fruity hop top note to amplify the Simcoe T-90 and Simcoe Cryo® dry-hopping. It makes sense to me to experiment by fractioning down those compounds that might increase bitterness (sesquiterpene fractions), harsh bitterness (humulene epoxides), musty aromas (humulene epoxides and sesquiterpenes), and earthy aromas (also sesquiterpene fraction)–especially when you consider so much of the oil is soluble compared to dry-hopping with pellets. The end result was great, a super punchy Simcoe-forward beer that doesn’t come across as extract-like, but seemed to just enhance the Simcoe already in the dry-hop. The reduced hydrocarbon makeup of the oil seemed to be a big improvement in terms of getting a truer-dry-hop-like flavor. 

In an all Motueka™ dry-hopped DIPA, we gave their HopBurst® Limonata (derived from Motueka hops) a shot. After fermentation and dry-hopping (4.4 pounds per barrel or ~17 g/L), we did some benchtop trials of different dosing rates and decided to dose the tank with 300 mL of Limonata. On the higher end of 500 mL (assuming about 19 bbls (2,229 liters) of beer in the tank) it was immediately brighter and bolder, but it started to move away from what I like about Motueka and got a little Dawn dishsoap-like and what I thought was a little bit more of a lingering bitterness. I kind of wish I would of ordered the HopShot® product (fractionalized to reduce some of the greener compounds) as it might have been better for this particular beer (and maybe most post-fermentation). On the lower end (300 mL) it seemed to liven up the beer, reduce a slight hop-spice thing it had going on.

We also trialed their Outback (Galaxy) HopBurst® oil in an IPA that was dry-hopped with Galaxy®, Hydra™ (Great Lake Hops), Vic Secret™. Hydra to is a hop that reminded me a bit of Galaxy in some sample packs we received, much like Vic Secret has done in the past, so we figured it would be a fun combination with the Outback oil. Again, I wondered if the fractionalized would have been better to lessen some of the green-leaning hydrocarbons because any dosing rate above 200 mL (again assuming ~19 bbls (2,229 liters) left in the tank after dry-hopping) started to change the fun fruit-striped gum aroma to a slightly piney one (albeit with a brighter overall aroma).   

Hopsteiner 

Talking with Dr. John Paul Maye, Technical Director at Hopsteiner, they currently use two methods to produce their post-fermentation oils. The various techniques for creating aroma hop extracts appear to be two main methods for making the oils. The first is steam distillation, which is considered the traditional way of making hop oils. Steam distillation takes leaf hops, boils them in water, condenses the vapor, and isolates the oils (this process is called oil type dry in Germany).

The second method of creating hop oils is called thin-film evaporation. During the process, CO2 hop extract goes through a thin film evaporator where the extract is under vacuum, and the oil is separated from the extract. One benefit to thin-film evaporation is the price (typically around $2/gram from Hopsteiner). The lower price is due, in part, to the ability to use a byproduct of creating the oils.

What compounds do these oils contain? Hopsteiner’s spec sheet indicates that for both thin-filmed and steam-distilled oils, the majority of the compounds are comprised of myrcene, humulene, caryophyllene, and farnesene (part of the sesquiterpene fraction) which makes sense when you consider these compounds usually represent a larger percentage of a hops total oils. However, if we consider the results of the charts above on how the individual compound classes of hops impacted taste perceptions, oils high in this sesquiterpene fraction might start to produce harsh bitterness, astringency, grassy, earthy, and musty flavors if used in too high of concentrations.

However, Maye also shared that some brewers were getting better flavor from the oils when they were added prior to maturation (so with some active fermentation still taking place). This concept makes sense to me as more of these more volatile sesquiterpenes would be removed with vigorous CO2 scrubbing, yeast, and other factors, leaving behind more polar and fruity compounds. In addition, by adding oils like Hopsteiner’s before maturation (and before dry-hopping) you may also get scrubbing of these sesquiterpenes by the leaf material coming from dry-hopping as the green material can absorb and remove many of these non-polar hop compounds allowing better flavor results from the oil.

Now, which one of these two processes (thin-filmed vs. steam distillation) is best for the hop oils themselves? I asked, Dr. Maye this exact question. “Some people like the thin film because it operates under vacuum and at temperatures hotter than 100°C, therefore it can pull-off more hop oil that steam distillation doesn’t. The only downside of thin distillation is the number of varieties is limited (because they have to already be in extract form) whereas steam distillation there is no limit.”

As I was preparing for this article, Hopsteiner sent me Centennial extract samples of thin-filmed and steam distillation samples. I opted to get the pre-emulsified versions (diluted 1:100 in propylene glycol) of each to make it easier to add them to individual kegs post-fermentation. I took 10-gallons of fermented IPA wort from a tank before dry-hopping and split them into two 5-gallon kegs. I added 3.5 grams of each oil inline as I transferred from one keg to another to help the thin-filmed and steam distillation oil mix evenly. This rate of ~.4grams/gallon (10grams/hL) is in the middle range of the end of their suggested use for ales. 

The impact was relatively subtle at this 10 grams/hL dosage rate for both of the oils. I think this is especially true when there isn’t any dry-hopping taking place (which I did in this case to get a better idea of how the oils perform). Neither of the oils screamed dry-hopped flavor to us at the rate, but there was a small difference between the oils. The Thin-filmed oil was slightly more subdued in overall aroma and had a slight botanical thing going on. The steam-distilled Centennial oil beer was a little more centennial-like and popped a little more aromatically with a slightly less grainy malt character coming through. 

At least for these two test beers, complete replacement of dry-hop character isn’t going to happen (which isn’t the point of them anyway). Although Maye told me that one brewer reported a mix of 3 ppm Lemondrop hop oil and 3 ppm Sultana hop oil resembled more of a typical dry-hop character, which potentially suggests the mix of oils may also be a good place to experiment with. Clearly, the dosage rate is going to have an impact on how much the oils shine, but at least for these samples, being closer to the 20 grams/hL seems like a better target. 

Glacier Hops Ranch Hopzoil™ 

Another potential post-fermentation hop oil extract on the market is from Glacier Hops Ranch called Hopzoil™. Similar to the extracts created from Hopsteiner, Hopzoil™ is more akin to a total oil extract, meaning the oil is more likely to resemble the hop it’s created from (but they are not trying to completely mimick the starting hop’s profile). Tom Britz, Founder and CEO of Glacier Hops Ranch, entertained some of my questions via email as I was trying to get a better sense of how their oils were created and how they might be best utilized. 

Tom explained that their oils are created by pure steam distillation from fresh whole hop cones after they are harvested. They see them as having a sensory benefit compared to making oils with pellets with supercritical CO2 technology. In addition to using individual hop variety oils, they also have created hop blends that target specific aromatic profiles, like the Citrus Fruitbomb™ I trialed in a small batch explained below. None of these oils, including the blends, contain alpha or beta acids. This is one area where Hopzoil™ is unique in that the lack of alpha-acids allows for potential use in the whirlpool without worrying about bittering. Although intended more as a cold-side hop product, I’m always a fan of the concept of trying to load up the fermenter with a diverse set of hop compounds to layer in hop saturated flavor to go with heavy dry-hopping. 

Tom also shared with me that the oils do, in fact, contain hop-derived thiols, which is intriguing as they can have strong impacts on beer even when dosed in small amounts based on their low sensory thresholds. Although the oils haven’t been tested that I’m aware for actual thiol counts (or thiol precersours), this is something to keep an eye on as a great way to get emulsified thiols into solution. I would be especially interested (and this goes for all the oils in the post) if any measured thiol precursors (discussed in a previous post) as those would be great candidates when paired with a GE yeast strain designed to unlock the thiols during fermentation. 

Just like with Hopsteiner, Hopzoil™ does come pre-emulsified which makes adding it to beer much easier as oil on its own would want to float and not extract into the beer. If you’d prefer to dilute the oil yourself, they also sell a “pure” format. Their “Majik” and “Hazy” line of oils are the pre-emulsified versions. 

In a video discussing a trial of Hopzoil™, it was estimated that 3/4-1 pound of hops equals ~4.5-5mL of oil (~a 4.5 x oil ratio). I like looking at this type of ratio to help get a sense of how many hops you might be using with oil. In terms of dosage recommendations, a good starting point is 2.5-5mL/BBL based on the discussions in the video. 

I tried dosing multiple 5-gallon kegs with different oils from Glacier Hops Ranch to get a sense of how they translate into fermented beer. I went super high on nearly 2.5x the suggested amount for the first set of trials to force their flavors a bit (especially after going too low on the Hopsteiner trials). All of the oils were again dosed into 5-gallon kegs of beer post-fermentation. We did separate addition of their Azacca, Amarillo, and Centennial oils for the trials, which all gave distinguishable characteristics. 

Although you can see what our customers who visited the taproom that particular day, the Amarillo oil was the most green and plant stem-like, which bordered a little oniony as it warmed up. I’m assuming the aroma of this particular one might be improved with a lower dosage rate or even active fermentation. Not relevant, but Amarillo has been a tough hop for us to use the past couple of yeast as it’s just not been up to the standard we were used to using only a handful of years ago (German Amarillo has been one of the better ones). The Centennial oil was one of our favorites as it had a nice bright orange character that stood out as the top note. The Azacca oil beer seemed to lighten/brighten up the beer, likely masking some of the doughness/vanilla character we can get from RVA Manchester, but it wasn’t particularly Azacca-like in any distinguishable way. 

We also did a 5-gallon trial of one of Glacier Hops Ranch blended oil offerings called Citrus Fruitbomb™. It’s unclear what hops make up the blend, but it’s advertised as an “explosively citrusy blend featuring several fruit-forward varieties.” In general, I’m always a little leery of hop blends of any kind because I can’t help to think they are blended because they aren’t selling on their own, but in this case, I’m interested as Hopsteiner found that when brewers were using multiple oils made from different hop varieties, the results mimicked a more authentic dry-hop character. 

For the F-bomb blend, we chose a simple pilsner base that was not dry-hopped, I again went a little high on the dosage, choosing ~.38 grams/gallon. I expected the aroma to be a little more potent at the dosage, but it was again relatively subtle. However, there was a difference from the base beer; the oils gave the pilsner an orange/lemon zest aroma. This particular beer had a noticeable mouthfeel impact from the oil, which I noticed in a few of the other trials at the brewery. There’s an oil slickness to the mouthfeel with a trailing extract-like resinous quality that sticks to the roof of your mouth after swallowing. To me, the aftertaste doesn’t read hoppy; instead, it reads extract-like. I’m sure adjusting the dosage rate might help with this, but likely at the cost of the citrus aroma. 

Other Market Options

It’s worth mentioning a few other companies that are creating hop oils (or will soon release), but I just haven’t had the chance yet to experiment with them. I had a good conversation with SORSE Technology in Sapwood’s tasting room about their hop variety-specific oils that will soon be available for brewers. Like with some of the other oils, they have a full spectrum approach, meaning the oil closely resembles that of the hop it’s created from. Unique to SORSE is their natural emulsifier, which avoids the use of propylene glycol. SORSE also has access to great hop varieties, so I imagine some of their future offerings will be appealing, especially if they decide to fractionalize to reduce some greener and harsher components. 

As I write this post, another company coming to my attention is Oast House Oils located in Lafayette, Colorado. Their oils are intended for cold-side flavor and created via supercritical CO2 extraction. Currently, they have oils available for Amarillo®, Azacca®, Cascade, Cashmere, El Dorado®, Huell Melon, and Mandarina Bavaria. A great Craft Beer & Brewing podcast with Brandon Capps of New Image Brewing dives deep into his experience with Oast House oils and is definitely worth a listen!

BarthHaas also has an oil product intended for a dry-hopping boost called Spectrum, which is available for Citra®, HBC 394 c.v. and Mosaic®. Spectrum is unique in that it’s advertised as being 100% from hop material with no emulsifier needed (contains ~30% water). Spectrum doesn’t contain iso-alpha acids or humulinones (it does contain polyphenols), so there’s no risk of additional bitterness. However, it does have some alpha-acids, so using it in the kettle could result in IBU pickup. BarthHass recommends first dosing the oil in 5-10 times the weight in water and stirred to disperse evenly. 

We’ve used the Citra® Spectrum product in a batch of triple IPA at Sapwood. In our experience, pre-mixing seems critical as dropping just a little bit in the water, the oil sank and remained in one solid chunk. It took a lot of stirring to get the oil to break up and homogenize in the pre-mix water. I could imagine this thick oil just sinking in your tank without trying to break it up first. We added the oil on day 3 of fermentation in hopes of dialing back some of the resinous and green extract-like characteristics you can get from these types of oils. I will say the Spectrum oil smelled better straight up than most of the oils we played with, perhaps because it’s 100% hops? Because we were using it during active fermentation, we weren’t afraid to go on the higher end of their suggested dosing rate of 0.5-1 ml oil per hL. We dosed at 500 mL of oil for a 20 bbl batch (2,347 liters). Because Spectrum is ~8% oil, our rate would be approximately 1.68 mL oil per hL. 

In this one experience with Spectrum, I think it did add a subtle bit of flavor complexity. Despite being used cold-side, the active fermentation addition seems to help reduce the harsh edges of the oil while providing the perception of hot-side flavor with just a little bit of an aroma push. We plan to continue experimenting with the rest of our jug in a future beer! 

Like with all these oils, figuring out how to use them (post-fermentation, active fermentation, or in the kettle), how much to add, and what beers might benefit from them is the challenge for brewers! So far, I see these oils as another tool, mainly for boosting dry-hop aroma by adding a top note to already dry-hopped beer. Or as a way to increase the saturated flavor needed to balance a heavily dry-hopped beer. I hope to see future papers looking even closer at post-fermentation hop oils and what exact compounds are being retained and at what levels. Particularly when it comes to thiols and thiol precursors as adding these with GE yeast strains in the kettle or at the start of fermentation could yield fun results! 

Cheers! 

Scott

Key Findings

• Post-fermentation oils can offer a last-minute hop burst without the risk of hop-creep. 
• Typically, hop oils are emulsified x100 the weight of oil with propylene glycol. 
• Hop oils may extend the shelf life of hoppy beers by reducing the amounts of staling aldehydes. 
• During a dry-hop with T-90 pellets, very little of the hydrocarbons (like myrcene) is retained, but the emulsified oils will likely be retained at much higher concentrations with hop oils. 
• When looking at hop oil fractions, monoterpene alcohols (like geraniol) increased the perceived sweetness, had a smooth bitterness, and was perceived as fruity (orange fruit, grapefruit, and lemon). In contrast, the sesquiterpene fraction of hop oil was associated with harsh bitterness and astringency. 
• Hop variety-specific hop oils made to mimic the overall oil profile of the source hop would likely come across more resinous, green, and astringent compared to normal dry-hopping thanks to higher retention of compounds like a-humulene, δ-cadinene, β-caryophyllene, β-myrcene, and caryophyllene oxide. 
• Dosing hop-oils that mimick the source hop oil makeup might be better used in the kettle or during active fermentation to help scrub the high concentrations of solubilized hydrocarbons. Oils that don’t contain alpha-acids can also be used in the whirlpool to increase hop oils getting into the fermenter without the bitterness increase. 
•  It makes the most sense to experiment with post-fermentation hop oils in small amounts in a glass and scale it up to dose the batch. Too little, and it seems like you don’t get much of an impact, but too much, and it can be detrimental! 

Below is a chart of some of the oils that are now available to experiment with!

Genetically Modified (GM) Yeast Strains: Unlocking Bound Hop Thiols and Engineering Targeted Fermentation Characteristics

led Image Courtesy of Omega Yeast

S

ettle in this one is dense, but I promise (or at least hope) approachable and engaging!

Often, when I get excited about a topic and can’t wait to experiment with data from the literature and write a post about what I learned (even if it takes me a couple months like this one). In that case, I think there is a good chance many brewers might share my interest in the topic. The GM yeast developments is one of those areas! There’s still so much to learn and explore, but early research and experimentation have convinced me that GM strains can be great tools for brewers to create complexity, new and exciting beers, and new hybrid styles. But GM technology is often approached cautiously, and for me anyway, the best way to form an opinion on something is to learn as much as possible about the topic. I did my best here to do exactly that, looking at GM technology, exploring GM yeast fermentation studies, interviewing the experts engineering GM strains, and reaching out to academic authors for guidance and clarification.

In this post, I explore the topic of genetically modified foods, in brief, to set the stage and create a context to how science is currently being investigated in beer and wine fermentations. I discuss some of the new genetically modified (GM) yeast strains that have been created to pull the curtain back on the how and why questions. I’ll follow up this post with more detailed experiences of these new strains as I have now had the opportunity to brew with them both in small-scale experimental batches as well as scaled-up batches. We even somehow convinced Bissell Brothers to try one of the strains out with us at Sapwood!

Genetically Modified Technology

To educate me for this post, I started first by reading (well, not really, I listened to it on Audible) a book titled Food Fight: GMOs and the Future of the American Diet. I mainly needed a refresher course on what genetic modification was, and this seemed like the only book I could find that was attempting to give both sides of the often-polarizing topic. The book opened by discussing one of the first genetically modified foods approved by the FDA in 1997 called Flavr Savr (much longer ago than I would have guessed). Although flopping, the tomato was engineered to ripen on the vine naturally during transit but still tough enough to resist rotting and mechanical picking. Using science for the crop improvement process was new, and as far as I can tell, it went relatively under the radar. To be fair, though, I was 14 and more concerned with protecting my size 6  Jordan’s from the South Dakota snow than paying attention to the latest agricultural science breakthroughs.

Fast forward to the present day, and the term GMO has become politically charged and polarizing, likely for several reasons like the mistrust of big food businesses, the seemingly unnatural nature of GMOs, and the confusion of information and data out there, to name a few. Nobody comes here to read about politics, I get that, but as I experiment with and learn about GMO yeast strains, I feel like there’s going to be some passionate pushback as well as praise. To approach this subject, I felt like I needed to do a little of my research on its history and place in our society to understand and perhaps form an opinion on gene-altering technology.

Despite such high polarization of GMO foods, the reality is that globally, it is estimated that 70-90% of animals raised to eat are fed GMO foods. The middle of the grocery isles is littered with processed foods made with GMO corn and soybeans (think high fructose corn syrup and soybean oil). GMO foods have already found their way into some of the most sold beer brands out there today, thanks to GMO corn and corn syrup in American light lagers. However, there seems to have been fear or hesitation of introducing GMO foods into beer production initially, whether for marketing purposes or other reasons. The book mentioned above states that Anheuser-Busch in 2008 announced they would not buy any of the $100 million of rice grown in Missouri if GM rice was allowed to be grown anywhere in the state. This was mainly due to the potential cross-contamination of GM plants with non-GM plants used to produce their beer. I wonder if GM yeast strains being engineered today will be looked down upon by some of these more prominent brands already using related science in the grist side of brewing?

When it comes to GM technology finding its way into beer via yeast strains, some of the safety concerns that often are attributed to GMO farming seem distant. For example, a GM yeast strain doesn’t require potentially dangerous pesticides and herbicide spraying like GMO seeds might. These aren’t roundup ready-like GMOs. Instead, researchers essentially remove or add a targeted gene for a specific purpose (Ie. enhance certain esters, remove certain phenols, or enhance biotransformation potential). Although this distinction seems obvious, it also seemed worth pointing out.

Types of GMOs

GMOs are of two varieties, cisgenic GMOs involve only genes from the plant itself or a close relative, and traditional breeding techniques could also transfer these genes. The other type is transgenic, which means the transferred gene usually derives from an alien species that is neither the recipient species nor a close, sexually compatible relative. ⁵ As for GM yeast strains, some efforts are cisgenic GM strains because the gene pool is not being altered. In other words, a gene is not being transferred that is not naturally occurring in yeast already. We also see a transgenic approach with yeast strains with genes inserted from food-grade bacterial sources or deriving from plants to enhance biotransformation enzyme potential. Not to say one method is better than the other, as both are being utilized in beer and wine fermentations successfully.

Natural Selection Modification vs. Lab Modification

Genetically modified seeds have been used by farmers naturally for years by hand-selecting seeds or hybridizing seeds that performed the best to increase future harvests’ quality and volume. This would be what I view as more of a natural selection modification process, which is still a form of human intervention but in a slower holistic fashion. In a twisted way, altering genes in a lab speeds up this somewhat natural but not natural process. Mutations in genes happen naturally, but not with the precision and speed as labs can now perform with tools like CRISPR (discussed below).

Human intervention into new yeast strains is not new; work has been done to hybridize strains for several reasons like aid in aroma formation (like encouraging ethyl and acetate esters), faster fermentation, uptake of certain sugars, and the ability to ferment in stressful environments. ⁶ Hybridizing strains are a way to create new yeast strains with specific properties without using more controversial GM technology and likely a process more widely accepted. This is especially true when considering that lager yeast (S. pastorianus) is a natural hybrid between S. cerevisiae and the newly discovered S. eubayanus. ⁷ However, as I discuss later in the article, there are complexities to the hybridization approach in terms of unwanted or unknown fermentation characteristics that can be avoided with the more targeted GM technology.

Some brewers would prefer this slower and more natural approach to yeast gene modification. In an interview with NPR, Firestone Walker Brewing Co.’s brewmaster (and somebody I look up to) Matt Brynildson commented that we should slow down the direction in which some labs are going related to GM yeast strain engineering.

“The next thing you know, we might be making beer with water, a drum of the cheapest sugar source you can find, and yeast that makes all the flavors that we used to get from barley and hops. That just wouldn’t be fun anymore, If we allow GMO yeast, well, I could think of a hundred more things that I do or don’t want my yeast to do.” – Matt Brynildson, Firestone Walker

I, too, can see the skepticism in producing such expressive yeast strains that you could argue might take some of the romanticism and skill out of brewing. I also agree with this statement regarding what to ask for from these strains; I even suggest one potential avenue of gene modification at the end of this post. But whether we should be doing this is a separate question altogether. At the same time, I also cannot stop thinking about the potential of combining bioconverting enzyme-producing strains with fruit-forward ester-producing strains to create new and potentially explosive flavors and aromas. There’s also a question of where do we draw the line for the use of lab-produced brewing ingredients. For example, exogenous enzymes are already sold and used to alter the natural brewing process (both cisgenic and transgenic), whether for bioconversion (beta-glucosidase enzymes), removing chill haze and gluten (Clarity Ferm), or improving the conversion of starches into sugars (amylase enzyme). All the enzymes mentioned above are lab-produced and perform tasks that the yeast, malt, and brewing process cannot generally do independently. Some, like ALDC (Alpha Acetolactate Decarboxylase), used to limit the production of diacetyl are even produced by a transgenic fungus. 

In my experience with test batches of GM yeast strains (which I plan to discuss in more detail in future posts), the result has been more of a way to build in added complexity and less to replace other ingredients altogether. I’m more inclined to be fascinated with new developments and products in brewing research and often try to force-feed them into my brewing experiments. Sometimes I do this with success, changing an ingrained process point, and more often, I don’t see much of an impact at all, adjusting back to the norm. I guess what I am trying to say is that my excitement for GM yeast potential outweighs my reservations.

Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)

How are these GM strains being created? Gene modification of most yeast strains is being done with a genome editing technology called CRISPR (other methods also exist, as Berkelely Yeast started trials with CRISPR but now utilizes a different set of molecular scissors). The technology took a big step forward in the United States in 2016 when the Department of Agriculture decided it would not regulate a CRISPR-created mushroom. Researchers engineered the white button mushroom to resist browning by targeting a family of genes, which ultimately reduced browning enzymes by 30%.⁸

CRISPR is now being used across multiple industries for various purposes. What exactly is CRISPR allowing researchers to do? Discussed on a recent Master Brewers Podcast, Charles Denby author of a recent paper titled “Industrial brewing yeast engineered for the production of primary flavor determinants in hopped beer,” described CRISPR as a way for scientists to make targeted double-strand breaks in DNA. If there is a part of the genome that is desired to be cut, they can then supply an exogenous piece of DNA, and if that DNA contains similar sequences of the cut ends, then that new DNA can be incorporated into the genome of the new organism.

Bryan Donaldson of Lagunitas noted on the podcast above that there were notes of fruity loops and orange blossoms to the beers made with the modified strains. He went on to say there were good fruity flavors in there without green vegetal flavors, but there was something “fundamentally missing” in the hop flavor. Donaldson suggested that trying to replicate the thousands of hop compounds with two targeted compounds (linalool and geraniol) is not likely to happen. I would agree with this observation.

GM Yeasts in Fermentations

Although this is the first I’ve written about GM strains, and its presence in beer fermentation is relatively new, it’s been around longer than we all probably realize, just not in the alcohol consumption arena. Saccharomyces cerevisiae has an estimated 6,000 genes, and genetically modifying them for specific chemical production and pharmaceuticals studies and production is already being done.⁹

As it relates to the present-day GM development of yeast strains, each strain’s goal seems to rest in the pursuit of increased biotransformation ability (both with wine and beer ferments) or the suppression of certain unwanted fermentation flavors like unwanted phenolics. However, there seems to be an incredible amount of potential in other avenues of targeted fermentation characteristics.

The wine world has been a little quicker to embrace GM yeast potential (at least in labs). A paper dated back to 2004 successfully engineered a saccharomyces strain to improve L-malic acid degradation. Saccharomyces strains cannot typically degrade -malic acid from grape must. The strain was also found to slightly increase the volatile acidity, ethanol, and glycerol production in test ferments. Sensory tests also found a sensory impact by enhancing the aromas. These “malo-ethanolic” strains were looked at as particularly beneficial of fruity-floral wines and de-acidification of high-acid wines in cool growing climates. ¹⁰

Although the wine industry has been looking at GMs for some time, there’s been some resistance from winemakers to use them (as the one tested above didn’t go into production as I understand it). It’s unclear to me how many winemakers are using GM strains currently and they may even be looking at the brewing industry to see how the public and brewers themselves react to the new strains. Especially considering the move in wine circles is going natural, biodynamic, and no intervention. For example with natural wines (like orange wines) no yeast is pitched at all, rather, the natural yeast on the fruit itself ferments the wine (similar in ways to coolship lambic).

In 2007 wine researchers released a paper where the goal was to engineer a wine strain capable of releasing a significant amount of bound wine thiols by overexpressing the bacterial tnaA in S. cerevisiae which creates active beta-lyase activity. Inserting tnaA into VIN13 (wine strain) did result in significantly more bound thiol release than the VIN13 that wasn’t modified.¹¹ Sensory panels also found that the modified strain with higher amounts of now free thiols scored higher in passionfruit, grapefruit, and box hedge flavors. They did note that an increase in the sweaty and cat urine aroma was observed at really high 4MMP thiol levels, suggesting that there could be ideal thresholds for certain desirable flavors with each specific compound.

The authors of the paper state that “Based on our results, we suggest that the cysteine conjugate precursors are transported into the yeast cells, the enzymatic activity takes place inside the cells, and the thiol is released and removed from the cells, either through diffusion or through active transport.” In other words, the precursors from the grapes (or hops) are likely transported into the yeast cells, where the active beta-lyase activity frees the thiols.

To me, when using the results above when thinking about beer and hop ferments, it would make sense to try and get as many the hop-derived thiol precursors into your beer as possible for the start of fermentation. Suppose the activity is happening inside the yeast cell. In that case, it makes sense that adding it late into fermentation when most of the cells have flocculated would result in less of this thiol-releasing bioconversion. This is especially true when considering work done earlier in another wine study that found free thiols were detected after the first day of fermentation and peaked at the early fermentation stages. ¹² Meeting consumer expectations through management in vineyard and winery: yeast choice for fermentation offers great potential to adjust the aroma). Possible ways to introduce these bound hop compounds for engineered strains to thrive on could be via pre-boil/boil hopping, whirlpool hopping, and brew day dry-hopping.

Unlocking Bound Hop-Derived Thiol Potential in GM Yeasts

This post (and most of the researchers’ attention) focuses on releasing bound thiols (3MH and 4MMP) and not bound monoterpene alcohols like linalool and geraniol. Although these terpene alcohols have long been great markers in research for determining the hoppiness in beer and play a role in the final flavors of hop-forward beers, increasing these compounds just doesn’t appear to have the same bang for the buck as releasing bound thiols. Thiols are just so fruit-forward in their sensory attributes and, because of their low taste threshold, can have a much more significant impact on the beer than their terpene counterparts. Thiols have also become the hot topic among academic work the past few years, something I welcome!

I’ve written before on potential ways to release bound hop-derived glycosides (like linalool and geraniol), and I still see it as an exciting area of brewing hoppy beers. But the more we learn about thiols, the more I see these terpenes as complexity builders and not the headliner. Using a beta-glycosidase enzyme (to free bound terpenes) like AROMAZYME still seems worth exploring, especially considering that thiols and terpene alcohols can play off each other through synergy, generally enhancing each other’s perception. The other enzyme, beta-lyase, can free bound thiols that might have a more considerable overall effect and that is where GM yeast strains come into play.

What are the two main thiol precursors in hops? The majority of amino acid precursors in bound thiol hop compounds are glutathione-thiol (glut-thiol) and not cysteine-thiol (cys-thiol) conjugates. The majority of glut-thiol precursors in hops is unfortunate because current testing has only been able to free-bound cysteine-thiol conjugates with active beta-lyase activity, the enzyme required to free bound hop thiols (by way of the IRC7 or TnaA gene). The IRC7 gene is likely the best yeast-derived (cisgenic) gene candidate to access and help liberate bound hop-derived cys-thiol precursors. The amount of free thiols, like 3MH, in hops, is often in much higher concentrations than its free form, showing how exciting figuring out how to free them can be.

However, it’s worth noting that Berkeley Yeast has done experiments that freed glut-3MH precursors when overexpressing cysteine–S-conjugate lyases(C-S) lyase activity. Cysteine–S-conjugate lyases are part of a large enzyme carbon-sulfur lyase family, which have been isolated from rats, humans, zebra fish, and Arabidopsis thaliana (flowering plant). ¹³ I’ll be curious to see if further testing to release glut-thiol precursors is done by targeting and inserting the gene(s) responsible for C-S lyase activity in beer strains, but for now, the focus is on freeing the cys-bound thiol precursors through targeted genes.

A paper dated back to 2013 shows the beta-lyase enzyme inability to break down glutathione conjugates, but rather cysteine conjugates. The paper states, “Therefore, S-glutathione conjugates (also evidenced as precursors of thiols in wine) were not degraded in our experiments.¹⁴ In terms of hop variety tested here, the paper found that Cascade exhibited the highest potential of bound 3HA (by releasing cys-3MH). Columbus, Nelson Sauvin, and Saaz extract released less, but still 29, 23, and 126-fold higher than without the beta-lyase enzyme.

Interestingly, the study’s beta-lyase also released the skunky MBT thiol at high levels (0.584 ppm for Nelson and 0.454 ppm for Columbus), both well above the extremely low MBT threshold 0.0000044 to 0.000035 ppm. ¹⁵

The MBT results above show that the hop variety we are using with strains engineered to have the IRC7 or TnaA gene and subsequent beta-lyase activity can impact the beer positively or negatively. Ideally, it seems, we would want hops with high concentrations of bound cys-3MH, which could be freed to 3MH while also avoiding hops that could produce high amounts of MBT (like Nelson). It’s interesting to note that some commonly used strains in hop-forward beer styles have been found to have inactive IRC7. To be clear, traditional brewing strains can still have the IRC7 gene, it just might be a mutated version that doesn’t have any activity, showing where GM technology can come into play (by switching it on).

The focus isn’t entirely on the IRC7 gene; Other organisms also contain genes that code for beta-lyase enzymes. In an early demonstration of how transgenetic material can be used to increase yeast beta-lyase activity, researchers at the Australian Wine Research Institute inserted a gene from E. coli into a wine yeast’s genome and showed that it had a lot more beta-lyase activity than its parent strain. For example, in the paper above that tested Cascade, Nelson, and Saaz, the beta-lyase enzyme used was derived from apotryptophanase (TnaA) from Escherichia coli. Using a gene from Escherichia coli would be an example of a transgenic modified approach as the gene responsible for thiol biotransformation via beta-lyase activity is coming from a non-yeast source. In contrast, when changing a yeast strain by adding and overexpressing the IRC7 gene, this is a cisgenic form of modification because the IRC7 gene already exists in yeast strains (likely more wine strains).

In terms of wine fermentations, this particular gene (TnaA) was also found to free bound cys-4MMP precursors suggesting it might be an excellent gene for releasing both 3MH and 4MMP.¹⁶ Berkeley Yeast has taken a transgenic approach to engineering brewer’s yeast for extra beta-lyase activity. Tropics™, which is a strain discussed in the post, contains a food-grade beta-lyase. On the other hand, Omega Yeast with its thiol-producing strain is using the IRC7 approach (derives from yeast already), also discussed in the post.

What is the threshold of these thiols, and what are the concentrations in hazy, hoppy beers? In 2021 researchers found that after comparing six hazy commercial IPAs for hop-derived compounds compared to West Coast IPAs, found a significant increase with the hazy beers.¹⁷

Interestingly, however, the thiol concentrations in these heavily dry-hopped beers were below the threshold in both 3MH and 3MHA. The thiol 4MMP was found above threshold across the average of hazy IPAs tested, showing that there is likely enough free 4MMP in most hazy hop varieties (Cheater Hops as I like to call them) to get above the threshold to have an impact on flavor and aroma. However, when it comes to 3MH active beta-lyase activity is probably required to get you above the threshold to free bound cys-3MH thiols unless you are pounding the beer with dry-hops. This is where GM yeast strains can play a significant role in releasing bound 3MH, potentially setting up even more 3MH conversion. A side note from this study cited above is that the thiol concentrations were not impacted much after being centrifuged, suggesting they are much more polar than some of the greener and woody hydrocarbons from hops (like myrcene which was significantly reduced after centrifugation).

It makes sense to take a step back then and summarize what’s going on here with these modified strains. What is being added, taken away, and overexpressed? When it comes to biotransformation potential in the cisgenic approach, labs are adding the IRC7 gene and (in some cases) overexpressing it, meaning it’s there but with elevated levels of enzyme activity. Inserting this gene into a strain like a London Ale III equivalent not only adds the ability to release bound hop thiols in a strain that otherwise doesn’t have the potential, but amplifies. It also keeps the other desirable traits of a strain like London Ale III in place (mouthfeel, haze, attenuation, etc.). 

The same is true in the transgenic approach. Still, a lab is likely taking another source of active beta-lyase enzyme activity utilizing a protein deriving from another source like another microbe or plant. By inserting this non-yeast derived protein into a beer yeast strain (and overexpressing it), you are (like with IRC7) setting up the potential of releasing bound hop thiols. It seems that the transgenic approach may be a more efficient approach to act on the bound hop substrates, freeing a more significant amount. For example, in Berkeley Yeast’s trials with Tropics™, they measured more than a 100-fold increase in released otherwise bound 3MH than a traditional highly active strain IRC7 gene strain. However, new strains are still being developed and tested with the IRC7 gene. I can tell you through my own trials that the Tropics™ strain is not only performing on paper, but its sensory impact was obvious too, in a very good way.

How are labs like Berkeley’s finding other potential genes to experiment with that might have enzyme activity capable of bioconverting? There are programs available to researchers like BLAST (genomic alignment tool) to insert gene sequences and look for similar ones. For example, put in a beta-lyase sequence and look for similar amino acid sequences from different sources that encode other beta-lyases. This can help target researchers’ approach to what kinds of active genes could force the beta-lyase enzyme activity in ferments. Two enzymes with similar amino acid composition may have wildly different activities. Some will be active when produced in yeast and others will be inactive. For example, in the Berkeley strain case, they used this approach to find other active bioconversion genes. They had to try many different beta-lyases before finding one that was especially good at releasing thiols from
both gluthathionylated and cysteinylated substrates, which is even more impressive considering previous research was just freeing only the cys-substrates.

Potential for Thiol Precursors in Hops

In an email conversation with Aurelie Roland, who authored an excellent paper testing the different bound concentrations of both cys and glu-thiol precursors (results in the chart below), I asked if the heat from the kettle would be enough to help cleave some of the bound thiols. I’ve theorized before that maybe whirlpool temperatures might help to release some of these compounds, but that doesn’t seem to be the case. Roland explained that heating is not sufficient to break the chemical bond between cys and glu-thiol precursors. In other words, releasing bound thiols is solely a job for an enzyme. Other methods for accessing these bound thiols could occur with beta-lyase enzyme additions (not via yeast) similar to the addition of a glucosidase with AROMAZYME. However, I can say when using products like Scott Lab’s Expression Aroma, which is described to extract “aroma precursors in white grapes such as thiols,” has not had even close to the sensory impact as something like the Berkeley’s Tropics™ GM strain. It’s unclear to me what exact enzyme Expression Aroma is, perhaps it’s not beta-lyase?

I like Roland and his team’s work so much because the results show how much thiol potential is in hops that are not being utilized in traditional ale ferments due to lack of beta-lyase activity. Below is a chart of the hop varieties they tested, comparing the free and bound concentrations of 3MH and 3MHA compared to the bound cys-precursors. I didn’t include the amounts of bound glu-3MH and glu-4MMP because we learned earlier in this post the inability of the beta-lyase enzyme to break down glutathione conjugates. Although, you can see why Berkeley Yeast might be onto something in their trials freeing both bound categories. Why? Because Saaz led the pack with an incredible 20,678 ppb of bound glu-3MH! ¹⁸

Potential in Malt for 3MH Precursors

Surprisingly, hops aren’t the only brewing ingredient that has bound fruity 3MH thiol potential. In a paper studying thiols, it was found that 3MH was being detected in unhopped beer but not in unhopped wort, suggesting that malt-derived 3MH precursors are coming from the malt. ¹⁹ But how do we know what types of malts?

A study was done in France where the authors investigated 3MH and 4MMP thiol precursors in six-row malted and non-malted barley samples. They found that G3MH (a 3MH precursor) was higher in malted than non-malted barley, suggesting an in-situ formation during malting. This may be important because it indicates that malted grains over unmalted are beneficial when encouraging GM strains’ bioflavoring process. Compared to large percentages of unmalted grains, 3MH increases in the boil, with thiols from malt playing a more significant role than we would think. The current study hypothesizes that less than 3% of thiol precursors in malts could lead to more than 64% of 3MH in the final beer because of the evolution during brewing. ²⁰ I imagine this study done with a GM yeast strain with either an overexpressed IRC7 or other bete-lyase gene would see these numbers inflate even more.

It would be fun to see more research into what factors might be playing a role in 3MH precursors in malted grains. One theory is that lowered kiln barley might have more 3MH precursors than barley kilned at warmer temperatures (pale malts having more than crystal malts, for example).

While it’s unclear to me now the exact concentration of 3MH precursors in different malt types, the data supplied by Omega Yeast’s strain called Cosmic Punch™ (chart below) shows how efficient a GM strain engineered to free bound 3MH can be. Their to-be-named thiol producing strain (IRC7 overexpressed) fermented in unhopped wort freed an enormous amount of 3MH from just grain precursors, well over threshold for both 3MH and 3MHA. The chart shows how little freeing their British ale strain is capable of, likely the same for many other traditionally used strains for hoppy beers. 

What if you pair the results from Omega with the hops high in bound 3MH, would you get a beer with thiol concentrations that are much too high to be enjoyable? The answer is I don’t know and I guess it’s up to us to find out! I can say in test batches with Berkeley’s thiol driving GM strain which is also freeing an enormous amount of 3MH from malts, did produce an extremely aromatic beer with lots of tropical fruit (guava and passionfruit). I also paired the beer with hops high in bound 3MH, which likely drove the thiol count even higher. I will say, to some, the beer was a little white peppery or spicy as well as super tropical. 

I think there is a lot of experimentation opportunities for brewers here to figure out first, the profiles these strains can produce, and second, try to appropriately place them in recipes for building balanced and but highly aromatic beers. Maybe copitching them to build in a little more balance as possible example.

Side Enzyme Activity and Other Observations

How might adding or altering one of the approximately 6,000 genes in a yeast strain impact the other genes and how they operate? It’s not as simple as just inserting a gene and getting the outcome (and only the outcome) you desire. Enzymes are specific in their respective activity, so when you overexpress something, you’ll likely get more of everything that gene is doing (both good and bad). A great example of this is when Berkeley Yeast was going through trials on creating a thiol-enhancing strain called Tropics™. They initially repeated the work done by the Australian Wine Research Group and they found that TnaA beta-lyase activity can release bound thiols and convert tryptophan (an amino acid) to indole. This is something they already knew; however, they just didn’t anticipate the resulting overexpressed strain would release as much indole as it did.

What’s indole? Simply put, it smells like poop at high concentrations. Indole is likely present in both beer and wine fermentation at low concentrations. At these lower levels, indole can add to the complexity. In early Berkeley experimental fermentations with the beta strain using the wine group’s TnaA they were getting great tropical notes but also getting fecal notes over the threshold (as the chart below shows). After they figured out how to get rid of the indole, they eventually found a different food-grade beta-lyase, which is what they used to make Tropics™. I can attest after a few small test batches that the indole is gone and the strain is incredibly fruity.

Chart from Berkeley Yeast

Omega Yeast is nearing the release of their strain of a traditional hazy culture with the IRC7 gene both inserted and overexpressed to push the cisgenic biotransformational release of bound hop thiols above sensory levels. An obstacle for Omega was not in the form of indole but with elevated levels of sulfur compounds being produced, which can also approach sensory threshold in lagers and wheat ales. Laura Burns, Director of Research and Development at Omega Yeast, told me that “we are finding that the final version of this strain has elevated sulfur production, though it is cleaning up at the end of fermentation. We are working on targeting the right amount of IRC7 activity to enhance only thiols and make sure that these sulfur compounds don’t approach sensory levels.” I am excited to give the completed strain a run in the future!

Genetically Modified (GM) Strains vs. Traditional Hybridization

Just because a strain was created in a lab does not make it a GM strain; as mentioned earlier in the article, strains can also be mated together through hybridization. Yeast creation through hybridization well predates CRISPR creations but comes with its own set of challenges.

Why not just use this more traditional approach vs. the new GM engineering approach? Simply put, it’s not as targeted. Think of yourself as a product of both of your parents, you embody traits of both of them (probably some good and bad!), yeast strains are no different. For example, if you create a hybrid strain with a bioconverting wine strain and a hazy IPA strain, you’ll likely end up with a new strain with the IRC7 gene making it capable of releasing bound flavors. The new strain might also take on other aspects of wine strain like phenolic production, flocculation traits, alcohol tolerance, etc.

A great example of this is a hybrid strain Omega Yeast sent to Sapwood to test out mating a hazy IPA strain and a bioconverting wine strain called Maxithiol. The Maxithiol wine strain “has the ability to produce aromatic thiols which contribute to significant fruity esters of tropical fruit and passion fruit to the finished wine.” The idea, you get the same hazy, hoppy characteristics from the ale strain and the thiol-releasing capabilities from the wine yeast. A bonus, because it’s a hybrid strain and not simply a copitch, the difference is the hybrid will get you the same results in the consecutive batch it’s harvested and pitched into. In contrast, a copitch would likely see drift and dominance from one of the two strains used in the blend, ultimately changing fermentation characteristics in future batches.

How did this hazy/wine yeast hybrid perform? We noticed a few behaviors with the strain that we don’t see in traditional ale strains used for making hazy IPAs. The hybrid strain was more attenuative than what we were used to with the source strain, likely resulting from a more aggressive fermentation capability in the Maxithiol strain. This could be offset with processes or ingredients (mash temperatures or maltodextrin, for example).

We noticed in test batches of the hybrid strain that we couldn’t harvest the yeast in volumes we were accustomed to in normal ale fermentations. Usually, we can harvest yeast from a 10-barrel batch and have enough yeast for a couple of 20-barrel ferments of IPA and DIPA. With the hazy/wine hybrid strain, we found a remarkably high yeast health percentage (90%+). However, the yeast volume we got was nearly half of what we usually get with a traditional non-GM London Ale III strain, making it tricky to re-pitch into future batches as planned. However, I will say our referments with the yeast performed as expected. Again, it appears that Maxithiol is not as flocculant as our usual strain, another trait sneaking its way into the hybrid strain. Yeast taking longer to flocculate out like this in heavily dry-hopped beers can, in our experience, enhance the vegetal bitterness bite and distract from the juicy smooth NEIPA flavor we are after.

Our yeast cell counts (thanks to Michael Tonsmeire’s microscopic abilities) with our usual RVA Manchester Ale strain and the Omega’s hybrid strain varied greatly. You can see an incredibly high yeast viability rate in the hybrid strain, but the total pounds harvested is significantly less. More time cold could have perhaps sped up the harvest poundage (maybe at the expense of some yeast viability), but time is valuable in commercial batches.

The last thing I’ll say about (and I don’t even know if this matters at all) is that the hazy/wine hybrid strain was also very green at the time of harvest (picture below). It almost looked like it had hops in suspension, similar to doing a drop of the cone with yeast and hops present. This is more just an observation than anything.

I bring up our results with the hybridized strain because it shows clear advantages to the CRISPR GM engineering approach, which is much more targeted in its fermentation outcomes. The GM approach to creating new strains allows control (after understanding each gene’s role) of specific traits from other yeast strains or bacteria. For example, rather than creating a hybrid strain with Maxithiol and a hazy strain to get the IRC7 gene, the GM approach allows you only to insert this gene into the hazy strain, getting you beta-lyase activity without the other outcomes we experienced in the hybrid. This precision is enhanced even more when the gene itself inserted (or replaced) performs only one job. In other words, if inserting a gene that only produces a single ester and nothing else, you know that the new GM strain won’t have any other side activities. This sounds easier than it is, but it’s a helpful way for me to understand and appreciate the difference between the two different approaches to creating new yeast strains.

Traditional Strains with Beta-Lyase Potential

Does it have to be a GM yeast to be able to unlock bound hop thiols? A poster was released at the 2020 World Brewing Congress in a joint research project with white Labs and Oregon State University, looking at what potential yeast strains may have the IRC7 gene naturally with the specific mutations that may release bound hop thiols. They found the strains BE057 (third highest), BE062 (second highest), and BE088 (highest) did surprisingly have the gene and ability to bioconvert. The three strains were found to have significantly greater activity than a wine strain called MaxiThiol, which is selected because of its ability to release bound grape-derived hop thiols.

However, leaning on experimentation and discussion with Nick Harris from Berkeley Yeast, that even highly active IRC7 variants containing mutations in their trials were not producing beers with thiols at sensory levels. This is not to say that strains with higher levels of IRC7 activity cannot make distinguishable beers between a strain without the gene inserted. Using a strain capable of releasing any bound hop compounds should only help build complexity into a beer by increasing thiols into ranges close to or over the threshold. Even under the threshold, the now freed thiols may boost overall flavor through synergy with other extracted hop components. Again, I’m looking forward to testing Omega’s new strain in this overexpressed IRC7 area!

Although I’m excited to see where more of this experimentation goes, I’d love to see traditional strains with active IRC7 genes tested in beer solutions with hops with a higher percentage of bound thiols to see their potential played out.

ATF1 and the 3MH to 3MHA Conversion

Because this post hasn’t already been technical enough, there’s one more area I’d like to cover because it’s one I’ve been interested in for some time in seeing the benefit of increasing the hop-derived thiol 3MH for the potential for the passionfruit-like 3MHA thiol. The problem, what facilitates this conversion once we have 3MH present? Again, we can look at older wine studies to get a better sense of what is required to get this tropical conversion to take place. In 2006, wine researchers tested and confirmed that the ATF1 gene and subsequent enzyme activity are responsible for this conversion (particularly Atflp enzyme). In the study, VIN13 was used as a control and a strain constructed with ATF1 gene inserted and overexpressed. Although VIN13 converted 3MH to 3MHA on its own (~100 ppb in the solution), the strain with ATF1 was a monster producing nearly 700 ppb. ²¹

So this is great, right? We seem to have now the ability to use hops high in bound 3MH; we can ferment with GM strain designed to release the 3MH at high rates and incorporate an overexpressed ATF1 gene to convert the 3MH into 3MHA for passionfruit bombs, right? Not exactly; Berkeley Yeast did exactly that and found that ATF1 has a broad substrate range, so it acts on many different alcohols. So while it may acetylate 3MH to 3MHA, it also made a lot of isoamyl acetate and ethyl acetate when overexpressed. This again shows that although the enzyme activity is particular when amplifying an activity, it also boosts all the enzyme-related activity.

Not all is lost in the quest for yeast-driven passionfruit thiol creation, as Berkeley Yeast was awarded a grant from the USDA to identify acyltransferases that specifically convert 3MH to 3MHA. This is being done in collaboration with Thomas Shellhammer at OSU.

Omega Yeast’s POF- Project

Biotransformation via active beta-lyase activity-freeing bound hop compounds isn’t the only role for GM yeast strains. The goal is to insert and perhaps overexpress the gene responsible (like IRC) for bet-lyase in bioconversion strains. You can also replace genes inactive in other strains with active ones in the parent strain, ultimately changing the strain’s fermentation profile. Omega Yeast has been exploring this area by essentially turning off the gene responsible for creating spicy and clove-like phenols common in some Belgian and Hefeweizen strains (the FDC1 gene).

Replacing an active gene with an active one responsible for phenol production allows the other fermentation characteristics to shine, like fruity ester production that might otherwise be buried under all of the spicy phenolics. This would be another example of a cisgenic GM yeast because the gene replacement is being done by ones already found in yeasts (strains with inactive FDC1 gene replacing an active FDC1 gene).
Targeting and replacing an active FDC1 gene is something I welcome coming from somebody who has done many experiments copitching wine strains known for biotransformation ability with traditional ale strains. Although these test beers could have unlocked bound compounds from the hops in small concentrations due to enzyme activity coming from the wine yeast, any possible fruity result was hidden behind competing phenol production from the wine strain.

Specifically, Omega has released two strains to the public that use this light switch approach to turning off the phenolic FDC1 gene in a Belgian strain and a Hefeweizen strain. I’ve been lucky enough to brew with both of these strains on both the experimental and commercial batches. Although I’ll likely follow up this post with much more recipe/results from the strains mentioned in this post, I can say that overall, these two strains in our test are subtle complexity builders and not creating fermentation characteristics that completely dominate the beer. In other words, another tool in the brewing toolbox to help achieve whatever it is the end goal is.

We used the Sundew strain in a Sapwood/Bissell Brothers collaboration, the results of which are discussed in the Graining In a podcast hosted by Noah Bissell and Matt Robinson.

Below are the two strains now available from Omega Yeast with their description.

Bananza Ale (OYL-400) – Bananza’s ripe banana flavor boosts tropical character in beer. Bananza is great for dropping more banana notes into your pastry stouts, milkshake IPAs, fruited sours and other modern tropical fruit-driven styles.

Sundew Ale (OYL-401) – Sundew has luscious strawberry, passion fruit and stone fruit esters, which combine to support desirable notes in modern fruity hops. Sundew sets a great foundation for hoppy styles like juicy pale ales, west coast IPAs or hazy IPAs, or its jammy profile can be paired with more malt-forward stouts, mild,s and brown ales. Think versatile like West Coast Ale I (OYL-004), but jammier.

Commercial Yeast Strains Available

Because I’ve briefly mentioned different GM strains (and one hybrid strain) that have been engineered at times throughout this post, below is the list of strains that were the focus of this article and used in test batches at the brewery. The tasting notes are broad as I plan to follow up this post with detailed thoughts on the strains.

If you want to try out these strains, stay tuned for an announcement from Omega releasing their hazy/wine hybrid strain. Berkeley Yeast has informed me that they are selling Tropics™ if you reach out to them directly. If you give these a try, leave a comment telling everyone how you used the GM strain and what your results were!

Other Potential Avenues for Gene Modification

What other areas could gene modification with yeast strains be used in the production of beer? I don’t have a lot of great pitches (see what I did there?), but one area that came to mind when reading through some of the wine research is the potential for increased glycerol production from a GM strain. Although the increase in glycerol production (which can increase the viscosity and mouthfeel) in the 2004 wine study mentioned at the start of this article was slight (1 g/L), it does raise the possibility for high glycerol producing strains. Perhaps a yeast strain capable of producing considerable amounts of glycerol could increase the mouthfeel and sweetness perception enough in hazy IPAs to offset a lower final gravity, reduce caloric intake, and improve the overall drinkability. In my experience, hoppy beers finishing with high final gravities (1.025+) can taste great (in fact, I prefer them), but consuming much of them can be palate taxing. Getting the body and mouthfeel from glycerol while at the same time reducing the final gravity is something I’d like to experiment with.

However, it’s likely not that easy as modifying a strain to overexpress the glycerol-producing gene was tested successfully in wine, but it came with unintended consequences. The study found that test ferments created too much acetaldehyde, acetoin, and acetic acid as a side-effect of the overexpression. ²² . Showing how difficult it is to create these strains!

I’ve also been interested in cold ferments and the impact the reduced temperatures can have on thiol retention to make highly flavorful and aromatic IPLs. Test batches with a strain called Tum 35 with minimal sulfur production (which can compete with hop aromatics) produced a great IPL at the brewery in my opinion (although it seems customers don’t love the term IPL). This particular beer also is by far the beer that’s held onto its fresh hop character better than anything I’ve brewed before.

The science that inspired the test batches in this area found that brewed test beers with Mosaic hops at the onset of fermentation and measured thiols concentrations for 3MH and 3MHA. The authors found that almost twice the amount of 3MHA was calculated in the beer fermented at 59°F (15°C) compared to the one at 71°F (21°C) with a wheat beer yeast (Tum 68). Specifically, the tropical and desirable 3MHA (converted from 3MH) went from 4 ng/l to 8 ng/l at the lower temperature. This might not seem like much, but with a low threshold for 3MHA (9 ng/l), you can see why it’s important. ²³

I’m not sure if the greater amount of conversion from 3MH to 3MHA is due to the beer’s reduced temperature encouraging compounds to stay in solution or if the lower temperature is somehow impacting the enzyme active ATF1 gene. Either way, it would be fun to take lager yeasts like Tum 35 and insert an active IRC7 gene to see if the colder ferments help increase bound 3MH concentrations and potentially maximize conversion to the passionfruit 3MHA. Maybe we could make IPLs cool again if this is the case and not have to call them Cold IPAs to sell them! I’ll be testing out a GM lager IRC7+ strain from Omega to potentially get an amped up version of Thiol Driver!

Areas for Experimentation

Copitching strains like Berkeley Tropics™ strain or the soon-to-be-released overexpressed IRC7 strain from Omega with a known ATF1 high producer like Vin13 to encourage greater concentrations of 3MH and subsequent 3MHA levels than what a typical strain might be able to achieve. Better yet, inserting the ATF1 gene from Vin13 (not overexpressing it due to the previous tests in this area) and the over-expressed IRC7 gene into a hazy strain to accomplish this without the phenolics that could occur with the Vin13 strain.

Wine Hybrids is an obvious area of experimentation here to converge the science of earlier years of wine GM yeast production and more recent beer GM yeast science. Creating beers with heavy whirlpool additions of high bound 3MH varieties paired with active fermentation additions of either wine juice alone or juice and skins to increase the precourours even more while also adding another layer of wine-like flavors. New products like Phantasm Powder (pulverized freeze-dried wine grapes) could also be considered for even more thiol-enriching potential. Rather than dry-hop these beers, you could add wine juice early into fermentation to play up this hybrid beer even more and let the yeast do the rest! I may or may not already be trying this. Could Grape Ale be a thing? With your help, we can do this! Maybe age these in wine barrels with your preferred mix-fermentation strain for a year or two and see what happens?

Thanks!

I want to say thank you to both Omega and Berkeley yeast for sending samples of their hybrid and GM strains. I want to specifically thank Laura Burns (Omega) and Nick Harris (Berkeley) for answering question after question through emails and various phone conversations. It took some time to put their complicated and impressive work into a language I could understand and write about with a hint of confidence!

Cheers!
Scott

Key Findings

• There are two types of GM yeast created using CRISPR technology. Cisgenic GMOs involve only genes from the plant itself or a close relative, and traditional breeding techniques could also transfer these genes. The other type is transgenic, which means the transferred gene usually derives from an alien species that is neither the recipient species nor a close, sexually compatible relative. Both are being utilized in creating thiol-releasing beer strains.
• The wine industry has been researching and creating strains dated back to 2004, nearly 20 years before the beer industry.
• The enzyme beta-lyase is required to free bound hop thiols, specifically, the cyc-precursors (cys-3MH and cyc-4MMP). Cys-3MH precursors are found in a dramatically higher concentration than 3MH.
• The hop-derived thiol 4MMP is available in hops in its free state in much higher concentrations than 3MH. Thus, using hops rich in 4MMP (like Citra®, Eureka™, and Simcoe®) are better choices for dry-hopping where enzyme activity is not required to free bound thiols.
• Hops (like Calypso™ and Saaz) have a significant concentration of bound cys-3MH and are likely better suited for kettle and brew day dry-hop additions. Especially considering the enzymatic activity responsible for releasing bound compounds is taking place inside the yeast cell, likely requiring active fermentation to free the bound thiols (with GM or hybrid strains).
• The primary two genes used to create GM strains for biotransformation purposes are IRC7 and TnaA. Both allow for beta-lyase enzyme activity during fermentation to free bound thiols.
• Genes like IRC7 and TnaA can not only be inserted at elevated levels to enhance the biotransformation potential. However, this will also amplify the other traits the particular gene performs.
• Malt also has 3MH precursors, which can be unlocked with GM strains. Lowered kilned barley likely has more of these precursors (pale malts).
• The thiol 3MH can be converted to 3MHA (which has a passionfruit flavor), but this conversion requires the ATF1 gene, which is likely present in most strains but at different expression levels (the wine strain VIN13 converted more 3MH to 3MHA, for example).
• Unlocking bound hop-thiols is not the only use for GM yeast strains. For example, Omega Yeast’s POF- Project replaces the active FDC1 gene responsible for phenolic flavors with an inactive version of FDC1. This turning off of FDC1 prevents phenolic flavors from occurring during fermentation.

M. Reukaufii, a Nectar-inhabiting Wild Yeast with Biotransformation Potential in Hoppy Beer

Nectar specialist yeast like M. Reukaufii has been found to alter the composition of nectar to create fruity compounds to potentially increase the chances of pollination, can it amplify fruity notes in beer too? 

I

t’s great when the science and study from one research area gets applied and tested in a completely different realm. In this case, on the backs of researchers examining nectar inhabiting yeasts for pollination purposes, brewers are using their results to experiment with some of the same yeasts in an attempt to maximize and compliment hoppy fruit aromatics.

In this post, I do my best to navigate some of the academic work done on nectar specialist yeasts and their impact on nectar composition and, ultimately, pollinator attraction. I reach out to one of the leading authors in this field for a little help in understanding their excellent work. I then finally brew a few test batches with one of the more common nectar yeasts (M. reukaufii) and discuss the results and recipes and discuss biotransformation potential with commercial enzymes. 

What are Nectar-inhabiting Yeasts?

In simple terms, flowers contain nectar, which is a sugary liquid produced by the plant, which attracts pollinators. Naturally occurring in some of the nectar (or transported by pollinators) are what’s called Nectar Inhabiting Yeasts (NIY). These floral nectar yeasts and bacteria produce volatile compounds that can impact their floral visitors. For example, one paper found that the yeast in pollen produced volatile signals that may attract pollinators. ²

The “fermentation” done by nectar yeasts may help attract pollinators for many reasons, like warming the nectar, altering the sugars and amino acids, altering the nectar’s scent, and influencing the acidity (similar in some ways to how beer fermentation changes wort). ¹ Of the nectar-inhabiting yeasts studied, Metschnikowia reukaufii (M. reukaufii) is one of the most common. Bumblebees have been found to favor flowers colonized by M. reukaufii as well as spent more time on the flowers compared to yeast-free flowers. ^{1 1}

So what compounds are nectar inhabiting yeast like M. reukaufii creating in pollen that is attracting pollinators? Below is a chart of compounds tested in nectar ¹ that may be relevant when we are thinking about using the strain in the production of beer. 

Of course, the makeup of wort and nectar are entirely different, but I still find it interesting to see what compounds M. Reukaufii creates when fermenting glucose and fructose in nectar for potentially understanding and applying it in beer. It seems likely to me that (like most things in beer), it’s a complex set of esters and alcohols along with the potential biotransformation abilities of M. reukaufii that might contribute to its flavors when paired with other yeasts and hop compounds.

Biotransformation and Fermentation Potential of M. Reukaufii

I’m so far from an expert on any of this, so I reached out to Rachel L. Vannette, Ph.D. Assistant Professor Department of Entomology and Nematology University of California, Davis, who authored one of the papers looking at the different compounds created in NIY for some clarification and guidance on the topic of biotransformation capability of M. reukaufii. Vannette directed me to the recent work of some of her collaborators who sequenced the genome of R. reukaufii (MR1). She sent me to a site that shows active enzymes among a genome (in this case, MR1). Some of these enzymes do look functionally similar to beta-glucosidase as part of the Glycoside Hydrolase family. 

I like to think about releasing bound hop-derived compounds into two groups to keep things straight in my head. The first is the potential to free bound thiols, and the other the release of bound glycosides. Both pathways need separate enzymes to achieve biotransformation. This concept is similar to your mash, where alpha and beta-amylase enzymes are required to break starch down into fermentable sugars.

Enzymes needed for releasing bound hop compounds:

Bound hop-derived thiol release – β-lyase (3MH, 4MMP)
Bound hop-derived glycoside release – β-glucosidase (monoterpene alcohols like geraniol, linalool)

M. reukaufii has the MR1 gene, which is cited as having an active enzyme capable of releasing bound glycosides, not thiols. So what does this mean? If a hop has been found to have high amounts of bound geraniol and is used in the whirlpool and then fermented with an enzyme active yeast (like M. reukaufii), it’s possible to benefit from both the free geraniol as well as releasing additional geraniol from the hop. The release of bound geraniol could be even more important when you remember that geraniol is known to be bioconverted to β-citronellol during fermentation, with ale strains means going from more herbal-like geraniol to a more citrus-like β-citronellol. The more geraniol released into the wort (both free and bound) the more potential for this bioconversion!

Although the release of some of these bound monoterpene alcohols might not make a beer completely explode in fruit flavors, as was found in one study ²⁴ it does seem that enhancing the concentrations of some of these desirable compounds could at the very least add to the complexity of your beer and potentially increase synergy among other compounds.

So, getting back to nectar and pollinators, The Yeast Bay has isolated M. reukaufii and now sells it to be used to ferment in beer. The idea is that this nectar specialist yeast can help bump the sweet fruit aromatic characteristics of beer to attract bearded men similar to how NIY attracts pollinators in flowers (sorry, had to). As the Yeast Bay site suggests, the bumping of flavors from M. reukaufii could be by “enzymatically altering otherwise inodorous nectar compounds like glycosides,” which we now can see may be from enzyme activity found in the MR1 gene. 

The Yeast Bay suggests that to use the nectar yeast, its best to co-ferment it with another brewing strain because it can only attenuate 20-25% in brewers wort because it doesn’t utilize maltose (the primary sugar source in wort). In my little experience with M. reukaufii, I would suggest experimenting with co-pitching with a healthy saccharomyces strain. Although, it would be interesting to add glucoamylase to the mash to convert all the starch/maltose into glucose and then perform the fermentation with only M. reukaufii to see how it performs.  My first small batch experiment resulted in obvious acetaldehyde (which the chart above did find in nectar ferments). Perhaps the London Ale III strain I pitched with it wasn’t healthy or strong enough to clear up the acetaldehyde produced by M. reukaufii?

One of the other potential benefits The Yeast Bay suggests may come from fermenting with M. reukaufii is the softening of the the perceived bitterness of beer. I speculate if this might have something to do with the strains ability to quickly drop the pH of fermenting wort. In studies looking at the perceived bitterness perception in hoppy beers, it was determined that the higher the pH of beer, the higher the perceived bitterness, which is why I’m interested in potentially adjusting the final pH of hoppy beers to see how it can impact drinkability. As it relates to one of the experimental batches I did with M. reukaufii and Saccharomyces “bruxellensis” Trois, after a dry-hopping at a moderate rate of 8.5 ounces in 5-gallons (240 grams in 19-liters) the final pH of the beer was 4.41. This reading is a little lower than I’m used to seeing at those dry-hopping rates (we typically see final pH readings in heavily dry-hopped beers of 3 pounds per bbl+ (~12 grams/liter) in the range of 4.5+).

More tests would need to be done to see if M. reukaufii is a reliable pH dropper, but I wonder if that might play a beneficial role in heavy dry-hopped beers like DIPAs along with its flavor-boosting potential. It’s been my experience that slightly lowering the pH in some higher ABV and heavily dry-hopped beers make them a little more approachable on the palate. 

Final pH in a M. reukaufii and Saccharomyces “bruxellensis” Trois Co-ferment.

Both of these experimental batches utilized a relatively new hop called Riwaka. I’ve been a fan of Riwaka since having a single-hopped Riwaka pale ale from Hill Farmstead Brewery. Unique from most of the other varieties regularly used in hop-forward beers, I find it can have a fruity candied-grape character with a little spiciness (which can come across as diesely to some). Riwaka is also a variety (granted, I’ve only used it a handful of times) that seems to have strong staying power when used as late whirlpool addition. The staying power was especially true in an IPL we brewed and fermented cool with Tum 35. Perhaps the lower fermentation temperature, combined with the lower whirlpool temperature, helped retain more of Riwaka’s volatile compounds. 

Riwaka has been a problematic hop to acquire (especially for commercial brewers), but as my luck would have it, Kemsley Eggers of Egger’s Hop Growers reach out to me after reading the New IPA. After chatting with Kem on the phone about his farm in New Zeland, the challenges and perks of running a hop farm, and of course, a little hop science, Kem asked if Sapwood would be interested in brewing with some of his Riwaka. It’s a fun experience to interact directly with the farmer, especially one so interested in what brewers think of his years of hard work. Hopefully, we can keep the dialogue going with future crops and different varietals! 

Let’s get to some trials using M. reukaufii in hoppy beers! First, I’ll walk through a small batch experiment co-pitching M. reukaufii with Saccharomyces “bruxellensis” Trois. I’ll then give the recipe and results of a much larger commercial-scale batch with the M. reukaufii in collaboration with a local brewery.

M. reukaufii, and Saccharomyces “bruxellensis” Trois Recipe

Brewed: October 2020
Tasting notes: October 2020
Batch size: 5.5-gallon

Result

Four days after the start of fermentation, I took a quick sample and was already pleasantly surprised (of course, it was already dry-hopped with a modest charge of Riwaka). Already down to 1.024, I thought the beer smelled its best at this point. I got a big fruity note from it in a tangy grape way. I’m guessing that tangy brite note might be coming more from the small amount of M. reukaufii paired with the pineapple-like esters that can come with Sac Trois, but it’s hard to say for sure. There was a hint of the spice/diesel thing you can get from Riwaka, but it was the mildest at this stage compared to post-fermentation dry-hopping. 

The beer ended up dropping a few more points before I dry-hopped it again with Riwaka in a purged keg. I left the keg at room temperature for 5 hours before going into a cold room at 40°F (4°C) for a few days. Although I make a case for cool dry-hopping, it does seem that when the temperature is less than 50°F, it takes more agitation to get good extraction. I theorize that the cooler temperature encourages hops to drop to the keg’s bottom faster at these temperatures. After a number of these smaller batch experiments at the brewery (dry-hopping in the cold room), I’ve noticed that I expected more of an aromatic punch based on the dry-hopping rates used in these beers. Because of this, I’ve been keeping the keg at 10-15 PSI and swirling the keg multiple times throughout the day to try and get those hops back in the beer. 

After post-fermentation dry-hopping and carbonation, I was pleased with how the beer turned out but it could benefit from some tweaks. I still need to experiment more with Riwaka, but I think I might enjoy the flavor I get from it in the whirlpool and active fermentation dry-hopping. I don’t think of active fermentation dry-hopping so much as biotransformation hopping but more to alter a variety’s perception in the final beer, and Riwaka might be a good example of this approach. I preferred the dry-hop character from the early dry-hop addition compared to the post-fermentation flavor. To me, the active fermentation helped to push out some of the hop’s rough edges (spicy flavors), seemingly leaving behind more of the fruit-forward compounds. My guess without getting the beer tested for compounds is that the more volatile and woody/spicy hydrocarbons are being actively scrubbed, and the more soluble monoterpene alcohols are staying behind. 

If I did this beer again, I’d probably take the advice of my beer palate coach Spencer Love, and pair the early addition Riwaka with a more fruit-forward tropical hop to bring out what I like about Riwaka even more. It seems like doubling down on it post-fermentation helped exaggerate what I don’t necessarily like from the hop. I think the same would happen when pairing it with another dank, spicy, and sweaty varieties like Nelson Sauvin (I’d understand how others might actually like this flavor, however). Citra or Galaxy might be great choices to pair with a beer like this rather than the post-fermentation Riwaka addition. 

Sapwood Jailbreak Collaboration

One of my good friends going back to DC Homebrewer meetings is Rob Fink, who is now the Lead Brewer at Jailbreak Brewing Company in Laurel, MD. Unlike most homebrewers that moved to brew commercially, Rob still finds and enjoys homebrewing. After spending a week milling thousands of pounds of grain, cleaning out mash tuns, running CIPs, you can see how a weekend without stainless might be appealing. However, similar to my experience brewing commercially, he finds the smaller batch experiments are where he can scratch his creative itch.

After I posted an article on some of the latest research on “survivables” and hot-side hop flavor, Rob sent me a text late that night after reading it saying, “I have determined that we should collab on another hoppy beer ASAP.” Our goal, to throw a lot of bioconversion-related science at one beer and see what might stick!

The beer, ultimately named Sisyphean Task, was eventually brewed and canned at Jailbreak’s facility. We decided to get some supporting bitterness with Warrior extract; when an IPA is as big as 9%, it needs a little balancing bitterness, in my opinion. We then layered in hot-side hops that new science suggests are better at providing hop-saturated survivable flavor. Mosaic and Idaho 7 were added to the whirlpool after cooling, and then we added a 3MH-rich hop in Columbus to the fermenter at yeast pitch. To boost hop thiol potential, we added Scott Lab’s Revelation Aroma, a β-glycosidase active enzyme, to potentially release bound hop glycosides. In addition, we added Scott Lab’s Revelation Rapidase Expression Aroma, which can potentially release bound hop thiol compounds. Both enzymes were added at yeast pitch with the Columbus Cryo® dry-hop. We also hoped that adding Columbus during active fermentation might help push out some of the more volatile hydrocarbon compounds that can lend more resinous, green, and spicy flavors and aromas (similar to what happeend to the Riwaka above). 

To take the bioconversion goal one more step forward, we also co-pitched the beer with M. reukaufii for its flavor-enhancing ability (whether through ester production or enzymatic activity). Rob had been experimenting with M. reukaufii with some smaller batches in various contexts, but mainly in hoppy beers in an attempt to achieve its advertised potential of increase fermentation expression of hop-derived flavors. Mainly, Rob had co-fermented M. reukaufii with yeast strains such as Conan or Wyeast’s West Yorkshire, which alone can provide excellent stone fruit esters, but the amplification from M. reukafuii was something he was enjoying. 

Rob has used M. reukaufii a half dozen times and finds that he notices its absence more than its presence. When co-fermenting with Conan, he can tell there is a higher level of yeast complexity and potentially more synergy among hop and fermentation compounds. 

Of course, when you are doing so many different things at once, like using multiple hop varieties, experimenting with more than one enzyme, co-pitching yeast (especially one originating from nectar), it’s challenging to know what exactly is doing what in the final beer’s profile. Sometimes, it’s just fun to layer variables and processes inspired by the research and see what you get. This experimental to the max approach is kind of what makes collaborations so fun! 

Sisyphean Task Recipe

Brewed: October 2020
Tasting Notes October 2020
Batch Size: 5.5 Gallons

Result

I like to rib Rob occasionally for his expansive vocabulary and pontificating skills, especially when discussing beer (mainly because I don’t know what he is saying). But, I have to admit, it does make the beer sound incredible. Because of this, I’m going put word-for-word Rob’s description of the beer he sent in an email before canning day because it’s so great.

“Early into fermentation, the ester production was reminding me a lot of a hot kveik fermentation, where the esters can get excessively tropical, in a one-dimensional sense. As fermentation wore on, that character was modulated quite significantly, and it eventually became harmonious, multi-dimensional, and, to be honest, quite compelling.

The body is rich without appearing on the palate as excessive or sweet. A cornucopia of fruit character (with no fruit added), simultaneously tropical (overripe, musky passionfruit) and brightly citric (caracara orange, ruby red grapefruit),

 

 

Overall palate expression is a vivid portrait of hop character and the complexity of fermentation, the latter of which is derived from a combination of thiol-enriching enzymes, a nectar yeast cultivated from brambleberry bushes, and conventional English ale yeast. Grist mostly comprises malted wheat, flaked oats, and raw wheat establishes a soft, incredibly silky foundation for the dry-hop assault of Riwaka, Strata, and Citra cryo.”

Is it worth using commercial enzymes in an attempt to increase biotransformation potential?

It’s tricky to say; I’ve talked to some commercial breweries who do it and think they get a little more flavor-retention in their hoppy beers when they use it. Others don’t seem to think it’s doing much for them. 

We can look at the results from a 2020 MBAA paper that tested whether using exogenous enzymes prepared for either hop-derived thiol or glycoside release impacted a hoppy beer. Using Galaxy and Enigma for the dry-hops, the enzyme-treated beers were put in front of a sensory panel, and the results were surprising. The glycoside releasing enzyme created a beer that was more herbal and resinous compared to the control beer. Similarly, the thiol releasing enzyme created a more resinous, berry, and vegetal (onion/garlic) beer compared to the control.²⁵ Side note, the authors of this particular paper just happen to be great dudes and worked hard at translating my book into Spanish, which should be releasing soon!

So at least in the case of Galaxy and Enigma, the enzyme-treated beers certainly did impact the beer but made them lean a little more herbal and resinous rather than amplify the fruitiness. I tend to think that glycoside-freeing enzymes would have less impact on flavor than thiol releasing because of the low taste threshold of thiols. There will hopefully be more studies like this in the future. However, I think there is still potential for enzyme usage, especially with hops tested to have high amounts of bound thiols and monoterpene alcohols. 

Lallemand has recently released an β-glucosidase enzyme called AROMAZYME specifically to be used in beer (most of the enzymes are directed at winemakers). They sent Sapwood a small sample of it for us to experiment with, and we put it to the test in a split batch experiment. I took ~16 gallons of wort from a 20 BBL tank the day after pitching the yeast and added AROMAZYME to the 16-gallons to see how it might impact the flavor from the hot-side hops (Amarillo and Mosaic). Both Mike and me were able to tell the difference between the beers. The beer that fermented with AROMAZYME was a little more complex, brighter, and punchier with a slight banana tropical thing to our palates. The beer that fermented without the enzyme was a little more “from the bag” hop character, which tends to be greener. It would be interesting to do this again, but to get the samples tested for actual compounds. 

One potential reason our results differed from the MBAA study could lay in the different hop varieties used and the potential for enzymes based on their respective bound compound composition. For example, one study investigated glycosidically-bound flavor potential in beers made with the 42 hop varieties. Using a commercial β-glucosidase enzyme to release the monoterpene alcohols, researchers found that Amarillo® showed the most glycosidically-bound geraniol potential. Mosaic was also found to test high in bound geraniol (as were Bravo and Chinook), which was the other hot-side hop we used in our experiment.²⁶

The difference between the two beers in our experiment were subtle, but I do think the enzyme-treated beer provided a better base for the tropical-leaning Vic Secret planned for the beer. But, knowing that some hops might do the opposite, as was found in the MBAA paper, it’s evident that more experimentation is needed! Part of what makes brewing so fun for me is using the brewing literature as a basis for experimentation. Whether it’s taking a natural wild yeast like M. reukaufii or playing with commercial enzymes for biotransformation, it continues to be one of the more exciting areas of hop science to me! 

Can a Once-Forgotten (and Lost) Lager Yeast Be a Good India Pale Lager (IPL) Strain?

Tum 35 was a popular lager strain until the 1950’s until it virtually went extinct. Resurrected in 2019, the strain shows promise as a soft, neutral, and low-sulfur producing IPL strain. 

I

‘ve only brewed a handful of lagers throughout my entire homebrewing career (not counting copitched lager beers). We’ve brewed a few now at Sapwood, but Mike mostly came up with the recipes based on his much more extensive lager brewing history. I think I’m just sensitive to the sulfur-like aroma many lagers can have, which I feel can distract from the style’s otherwise grainy and clean characteristics. Even when throwing hops at a lager, I still find this “lagery” flavor somewhat competitive for the hop-derived flavors I’m after. 

Despite my preference for ales, I have done a couple of unique lager strain experiments (mainly through the inspiration of my friend Spencer Love) like a Rice Saison Lager and Thiol Driver (a lager/wine yeast copitch beer designed to take advantage of the science of synergy and biotransformation). One of the reasons I’m so intrigued by lager ferments, however, is the potential increase in hop-derived compound retention that low-temperature ferments can provide (more on this later in the post). 

When I read a newly published paper from BrewingScience about a resurrected lager strain (Tum 35) with reportedly no sulfur aroma and ability to ferment as low as 50°F (10°C), you can see why I started to get excited again for some more lager and hop experimentation! 

This post explains some of the history of the discovered (again) lager strain Tum 35. I then brew (with the help of some friends) some test batches with the strain after getting a yeast slant mailed from the author of the paper in Germany (who also permitted me to write about the results). Lastly, I then brewed an India Pale Lager with Tum 35, the reason I was excited about the strain in the first place! With the help of a commercial enzyme to unlock hop-derived thiols, science into selecting the whirlpool hop varieties, and the cold fermentation ability of Tum 35, I attempted to push the aromatic thiol flavors as much as possible without the “lagery” flavors getting in the way! 

Tum 35 History

All of the historical information in this post comes from the study referenced below titled, “Resurrection of the lager strain Saccharomyces pastorianus TUM 35.” 

The Research Center Weihenstephan for Brewing and Food Quality (BLQ) is an institute of the Technical University of Munich (TUM) and where these strains are studied and banked (thus the TUM names for the strains). Let’s start with Tum 34 as it’s the most popular lager strain used in the world and one of the first bottom-fermenting strains to be sequenced and published.²⁷ While Tum 34 may not sounds familiar, Frisinga Tum 34/70® probably does ring a bell (often referred to as 34/70 Weighenstephan 34/70, W 34/70). 

The lager strain Tum 34 started to become the dominant player in the lager game in Bavaria, Germany, in the later 1950s due to its superior ability to flocculate and produce clean beers despite lousy weather at the time producing unreliable malts low in amino acids and soluble proteins. After World War II, however, Tum 35 was one of the more common and widespread yeast strains used in Franconia (northern Bavaria); it was then referred to as “C” because of the city and brewery of it’s use-Hofbrauhaus Coburg. At the time, beers brewed with Tum 35 were described as “mild, balanced flavor, and fine notes of hops.” 

As mentioned, bad weather in the early 1950’s started to produce less than ideal grains used for brewing. The weather seemed to have the most significant impact on the Tum 35 strain, as brewers were having a difficult time harvesting the lager strain as it would stay in suspension much longer than others (even after crashing). In fact, of all the strains used at the time, Tum 35 was reportedly one of the worst flocculators. Frustrated, brewers started to turn away from Tum 35, despite enjoying their characteristics from the strain. Bavarian lager brewers began to use other more reliable harvesting strains like Tum 44 and eventually transitioned to Tum 34 because of better-reported flavor consistency. 

Tum 35 was completely forgotten about from the late 1950s to the present day, only being used in 1987 and 2002 in two published strain comparison papers (by Donhauser et al. and Wagner). Tum 34 wasn’t even active as a slant agar or cryo stock culture. So, after that last use in 2002 for academic purposes, Tum 35 was essentially lost; fortunately, a forgotten box in a storage room was recently found at the Institute of the Technical University of Munich that was marked “35.” The researchers were able to reactivate the yeast from a dried pellet in liquid wort and confirm it was, in fact, Tum 35. 

Tum 35 Studied 

After finding the forgotten lager strain in a box and resurrecting it, the researchers began putting the strain to the test against other lager strains. In their 2019 paper, the authors brewed an ~8 gallons (30 L) test batch where fermentation was done at 52°F (11°C) for 13 days with a diacetyl rest to follow. After subsequent lagering for two weeks, the beer was put in front of a trained tasting panel where the results were compared to 480 other lager beers tasted by the tasting panel throughout 2018. 

Tum 35 preformed admirably as the comparative results showed the strain was above average in flavor, taste, and quality of bitterness. The panel described the beer fermented with Tum 35 as “pure and delightful, fresh and yeast-typical, full-bodied with a slight bitterness, well balanced and soft.” Most interesting to me, the strain was determined to have no sulfuric aromas that are often typical of lager strains.²⁸

With a low sulfur-producing lager strain that can be fermented cool, has a soft and full-bodied mouthfeel, and tastes “delightful,” you can see why I requested a sample be shipped from Germany to start experimenting with! After delays due to the COVID, which impacted the needed certificates necessary for delivery to the USA, I eventually got a yeast slant in the mail. 

Having never propped up a strain from a slant, I sent the Tum 35 (now called and referred to as JY268 Franconia strain) to Jasper Yeast in Virginia. Jasper banked the strain for future use for us (and you!) to use at Sapwood and built up a pitchable culture for me to experiment with for this post. If you are interested in experimenting with the Franconia lager strain, you can reach out to Jasper to get a pitch. I’m curious what others might think of the strain! 

Hop-Derived Fruity Thiols and Cold Ferments

Before I go further, I need to explain a little science that has me so interested in a lager strain with NEIPA-like mouthfeel descriptors. A 2017 paper experimented with how different fermentation temperatures might impact the retention of more hop-derived fruity thiols. Thiols have very low taste thresholds, so even small amounts of retention could have a significant aromatic impact on beer. I talked a bit more about thiols midway through this post on hot-side hopping if you are interested in more background thiol information. In this case, the authors found that the colder a beer fermented, the more retention of hop-thiols remained in the beer. 

Specifically, the paper mentioned above brewed test beers with Mosaic hops at the onset of fermentation and measured thiols 3MH and 3MHA. The authors found that almost twice the amount of 3MHA was measured in the beer fermented at 59°F (15°C) compared to the one at 71°F (21°C) with a wheat beer yeast (Tum 68). Specifically, the tropical and desirable 3MHA (which is converted from 3MH) went from 4 ng/l to 8 ng/l at the lower temperature. This might not seem like much, but with a low threshold for 3MHA (9 ng/l), you can see why it’s important. 

Also, because 3MHA is converted from 3MH, it’s equally important that the 3MH concentration also increased when fermented at the cooler temperature going from 31 ng/l to 37 ng/l.²⁹ Obviously, the more you can push the 3MH the more potential for 3MHA (especially with the right yeast strain or with a commercial enzyme). 

So, what if we take advantage of low temperature fermenting lager strain to potentially retain more fruity hop thiols from the hot-side whirlpool hop additions as well as add a commercial enzyme to the wort to increase thiols even further potentially.

Before I go straight into brewing the test India Pale Lager with the Franconia strain, we put it to the test in some more standard lager worts with some friends’ help. This way, we all got a more hands-on sense of how it compares to other lager strains we’ve brewed with in the past. It’s also just nice to not rely entirely on the academic sensory results. 

Tum 35 Test Batches

First, my good friend Trevor Fisher brewed a split batch experiment with his Grain Father. Here, he brewed two identical lagers, but one was fermented with Tum 35 (built up from Jasper) and the other with Tum 34 (34/70 dry yeast packet). The recipe was inspired, in part, from an Oxbow beer called Luppolo, which is a lightly dry-hopped unfiltered lager.

After fermentation and four weeks of lagering, I went over to Trevor’s house to do a blind triangle test of the beers while he still had them on tap. I was served two samples of the 34/70 fermented beer and one sample of the Tum 35 (Franconia) fermented beer. I was able to detect the odd beer out. For me, it was both in the aroma and taste where the beers were distinguishable. 

Left 34/70 | Center 34/70 | Right Tum 35

As advertised, the distinguishing trait in the Tum 35 beer was a less “lagery” aroma (I’m already a fan). The 34/70 beers had a fruity green-apple-like mid-palate that wasn’t in the Tum 35 beer. Overall, the Tum 35 beer was more neutral, with a little more noticeable minerality and softer mouthfeel. The aroma from the Tum 35 beer seemed to be coming mainly from the pilsner malt used. There was very little yeast-derived fermentation flavors/aromas that I could detect. There was a little more alcohol hotness in the 34/70 beer, likely due to a two-point lower attenuation from the Tum 35 beer. Trevor got a final gravity of 1.010 with 34/70 and 1.012 with Tum 35. Of all the test batches, Trevor had the best luck getting a lower FG with Tum 35, perhaps we should of all pitched closer to his rate of 200 mL of slurry into 3.5 gallons or wort with elevated fermentation temperatures! 

Spencer, who brews an easy-drinking lager once a year to take to a lake cabin to consume with his friends responsibly over a weekend, also tested out Tum 35 with his lake rice lager for the year (it’s also the slurry I used for the IPL in this post). 

Spencer’s lager was another excellent example of how Tum 35 can be a slow fermenter, especially at colder temperatures. For his rice lager, he maintained 50°F (10°C) for the entire ferment, not even rise at toward the end of fermentation (something he would do the next time around to help it finish out a little quicker and perhaps lower the gravity). The beer eventually achieved 68% apparent attenuation, but it took a while. For example, the following are his gravity readings throughout the ferment. 

————————–

Tum 35 Rice Lager Fermentation Readings

Starting Gravity: 1.041

5 days: 1.034

8 days: 1.024

11 days: 1.016

15 days: 1.014

19 days: 1.013 (FG) 

————————–

Spencer’s results (like ours at the brewery with Tum 35) suggest that a good big healthy pitch and slightly warmer temperatures are probably best to get the strain to finish in a more reasonable time frame. After our test batch experience, I’d probably start Tum 35 at 52°F (11°C) and gradually ramp to 58-60°F (14-15°C) over a week or so. It doesn’t appear to be the most attenuative strain either (which can be a good thing depending on your goal) as the rice lager finally finished at 1.013 but was mashed low at 149°F (65°C). Maybe even having an active starter and larger yeast pitch would help (this was from our commercial pitch that sat around awhile before using). 

Overall, Spencer’s sub 4% Tum 35 lager was super drinkable. Head retention was decent but not spectacular. There was a more pronounced malt character than he was expecting (cracker, biscuit, and straw-like). Regarding the sulfury-lager notes, he too thought the strain was on the low end of the flavors. The cleaner ferment is probably why the malt flavors shined so much (something we found also).  

Both Trevor’s and Spencer’s recipes are available below. 

Tum 35 India Pale Lager Recipe

Brewed: August 2020
Tasting notes: September 2020
Batch size: 5.5-gallon 

Results

Now that I had the opportunity to taste a couple of Tum 35 test batches, I was excited to see what the strain could do in a low-temperature ferment with hops and enzymes designed to boost (and hopefully retain) fruity monoterpene alcohols and thiols.  

For the yeast, I pitched ~ 300mL of Tum 35 harvested from Spencer’s trials. I kept the beer at 50°F (10°C) for the first two days of fermentation, but with little activity seen in the airlock, I bumped (and kept the temperature) to 52°F (11°C) for 16 days before kegging and dry-hopping. 

Because I planned on pitching two commercial enzymes with this IPL for biotransformation potential, I also decided to add 2-ounces of hops at yeast and enzyme pitch to push the compounds that might be converted (paired with the low fermentation temperature this seemed like a good idea to try and retain and boost thiols). Also, the whirlpool additions were lowered to 185°F (85°C) in hopes of additional hop-derived oil retention and potential conversion. 

As for the whirlpool hop selections for this beer, Mosaic was incorporated as it was found to be a very high survivable hop, something I’ve become more convinced makes a difference for saturated hot-side flavor. In addition, it’s a variety we’ve continually found at the brewery to be a great hot-side hop in terms of carrying through some its flavor/aroma after fermentation. 

Regarding Nugget, a 2015 BrewingScience study looked at extraction efficiency of hot-side hops and tested for 59 different hop compounds for fifteen single-hopped beers. Of the 15 different hop varieties tested, those that imparted the most monoterpene alcohols were (in order of highest): Nugget, Columbus, Cascade, Centennial, and Sorachi Ace.³⁰ This is likely due in part to the high concentration of linalool in Nugget, one of the compounds included in the set of survivables studied by Yakima Chief. 

You might wonder why I used a slightly older (2018) lot of Nugget, I’m a fan of experimenting with slightly older hops in the whirlpool (along with fresher hops for greater overall complexity of compounds going into the fermenter). One reason is that a 2014 paper found a reduction in hydrocarbons as hops aged (these are the greener, more resinous, and woody compounds). In the study, five U.S. varieties (Columbus, Chinook, Nugget, Cascade, and Mount Hood) in bags were cut open and stored at room temperature or 32°F (0°C) and analyzed after four and twenty-four weeks for compound concentrations. The authors found a shift in the percentage of terpene hydrocarbon percentages. Specifically, in fresh hops, the terpene hydrocarbons accounted for approximately 85-95% of the hop oils; after twenty-four weeks of storage exposed to air at room temperature, the percentage dropped to 30-60%.³¹ Although these hydrocarbons are generally more volatile and likely have little staying power when introduced to boiling wort, I suspect at chilled whirlpool temperatures, they may be finding their way into wort at higher rates. 

Tasting the IPL two weeks after yeast pitch, I was thrilled with the amount of post-fermentation hop aroma and flavor. How much of this was due to the early 2-ounces of Nectraon, low-fermentation temperature, whirlpool hop additions, or enzymes is unclear. Still, there was a great mango, apricot, and jelly donut-like already before dry-hopping, providing a great hop saturated base layer for some dry-hopping! There was also a surprisingly high pH after primary and pre-dry-hop at 4.52 (unfortunately, I never recorded a post-fermentation dry-hop pH). 

Nectaron® (the experimental name was HORT4337) is a new promising hop from New Zeland that is described as super tropical and passionfruit-forward. After a few little test runs with it at the brewery, sampling a friends, and smelling from the bag I get a subtle Galaxy-like bubblegum thing, so why not pair them up! I want to experiment further with Nectaron® as well as get a glimpse into its oil data to potentially get a sense of when to best use the strain (whirlpool, early dry-hop, late dry-hop, etc.). 

For dry-hopping, I transferred out of the primary fermenter in a closed-loop into a purged keg (with a dip tube filter) and put back into the keezer at 52°F (11°C) for three days. Once a day, I would pick up the keg and give it a good swirl to encourage the hops to get back into suspension and extract (the keg was under ~15 psi of pressure during the dry-hop). After the three days of cool dry-hopping, I transferred to a purged serving keg and put on tap at ~38°F (3°C). 

Overall, I was pleased with this beer! As advertised in the literature and found in our test batches, Tum 35 produces very little of the lager-like sulfur aroma I’ve become sensitive too, which I think does allow the hops to stand out more. Despite the beer finishing sweet (1.028), it gives a much dryer and crisp impression but still a nice hazy IPA-like softness. Because Tum 35 appears to produce beers very neutral on the palate (not a lot of big fermentation phenols or esters), it then seems to enhance the flavors coming from the grain (probably especially at such a high final gravity). 

Whether it’s the slow fermentation retaining more hop-derived thiols, some biotransformation, neutral and soft Tum 35 ferment, or just some great hops, it was a solid IPL! Despite being sweet, it wasn’t as cloying as some hazy IPAs can be. To me, I could still slightly tell it was a lager, but it didn’t scream it like other IPL’s I’ve had. There seems to be some promise in this once forgotten lager strain. If our little bit of experience with Tum 35 is accurate, it seems to be a slow fermenter (taking around two-weeks to finish) and isn’t super attenuative either. Granted, in this particular beer, I mashed hot and had some maltodextrin. However, we just finished fermenting a Tmavé Pivo (Czech-style dark lager)and saw ~67% apparent attenuation when mashing at 155°F (68°C). 

This India Pale Lager test batch was good enough that we will be scaling a version of it up for an upcoming collaboration IPL brew with Astro Lab Brewing in Silver Spring, MD. Again, we’ll ferment with Tum 35, but mashing much lower (150°F (65°C)) to increase the attenuation. We also plan to eliminate the oats (just pilsner, malted red wheat, and chit malt) for an even more neutral base for a heavy Nelson Sauvin dry-hop and Riwaka and Wakatu whirlpool hops! 

Tum 35 Beer On Right

Survivables: Unpacking Hot-Side Hop Flavor

Why hops like Idaho 7 might be so good at imparting saturated hop flavor to beer

O

ne of the things I obsess with at Sapwood is tasting our hop-forward beers pre-dry hop. After a tank has been soft crashed down to 58°F (14°C) for a few days, we’ll dump or harvest the yeast and then dry hop. Right before dry hopping is the best time to pull a sample to determine how much hot-side hop flavor the beer developed. We are always trying different hop varieties in the kettle and playing with varying temperatures of whirlpool and duration, usually using some of the latest hop science as our guide to our experimentation. The only way to see what is working (and what is not) is to taste the beer and take good notes! 

One of the varieties we experimented with early on in the whirlpool was Idaho 7. Tasting these particular beers pre-dry hop I was consistently amazed at how much saturated hot-side flavor they had. In fact, one beer that was dry-hopped with Sabro, the whirlpool addition of Idaho 7 was walking all over the dry hop. Rarely can a hot-side hop addition overshadow a dry hop! 

In March of last year, I tweeted that I thought Idaho 7 was the greatest hot-side hop I’ve used and guessed it was likely because of polyfunctional thiols or hop-derived esters, but had no idea why it was so effective. Luckily for us, Yakima Chief Hops has just put it to the test, and we now why Idaho 7 (and a few other varieties) are likely so great at imparting hot-side flavor! 

Don’t tell anyone, but Idaho 7 is one of the greatest hot-side hops I’ve ever used. I don’t know the science yet (maybe thiols or hop-derived esters), but the amount of tropical hop saturated flavor pre-dry hopping is unreal compared to other varieties.

— Scott Janish (@ScottJanish) March 24, 2019

Before jumping right to the latest research from Yakima Chief, I thought it would be helpful to take a step back and look broader at some other research into hot-side hopping to help make sense of it all! So, in this post, I start by breaking down the various hop compounds into the classes that I believe are the most useful when trying to determine hop flavor potential in the kettle. The first class of compounds are oxygen-containing monoterpene alcohols like linalool and geraniol. The second class are hop-derived esters and fatty acids. Third are polyfunctional thiols like 3MH, 3MHA, and 4MMP. I then try to compile a list of hops that the science suggests may be good candidates to experiment with to try and push as much hot-side flavor as possible. 

You’re probably thinking, “why didn’t you include hydrocarbons in the list?” Nobody is actually thinking that, but in case you were, even though hydrocarbons can make up 40-80% of the total oil of hops, I decided to leave this class of compounds out of this hot-side discussion because they are so volatile. Myrcene (a hydrocarbon), for example, has been tested to be reduced 50% with just ten minutes of boiling and completely removed after a full 60-minute boil. ³² Whereas geraniol (part of the oxygen-containing monoterpene alcohol class) has a higher boiling point and more likely to find it’s way into the fermenter. Hydrocarbons likely play a more significant role in dry-hopping, especially post-fermentation dry hopping because even active fermentation can scrub these volatile compounds. 

Oxygen-Containing Monoterpene Alcohols 

The oxygenated components, which represent about 30% of the total oil, is a very complex mixture of alcohols, aldehydes, acids, ketones, epoxides, and esters. Most important to brewers looking for intense fruit-forward IPAs are the terpene alcohols located in the oxygenated fraction of hops (examples: linalool, nerol, geraniol). Despite representing a small fraction of the hop, they are more likely to remain in beer throughout the brewing process and are less volatile than terpene hydrocarbons such as myrcene.  

One paper found that hydrocarbons have very low solubility compared to the fruiter oxygenated monoterpenes. Specifically, the paper found that monoterpenes containing oxygen in the form of a ketone, alcohol, ether, or aldehyde had solubilities 10-100 times greater than hydrocarbons.³³ However, it’s important to note that even though monoterpene alcohols have more staying power, they are still volatile. Linalool has been tested with losses as high as 80% in just five minutes of boiling, suggesting whirlpool hopping is your best bet to try to preserve these compounds. 

To put a finer point on this, a 2017 paper released by the Journal of the American Society of Brewing Chemists tested how whirlpool additions are impacting hoppy beers.³⁴ Here, beers were brewed with Simcoe at either 60 minutes, 20-minute whirlpool (right after the boil, no cooling was done), or a dry hop addition only (for 48 hours). In terms of measured concentrations of hop-derived volatiles in the finished beer, there was a clear winner with the whirlpool beer, which was measured higher for linalool (flowery-fruity), α-terpineol (lilac), geraniol (rose), and β-citronellol (lemon, lime). A sensory panel could also detect a difference from the control beer in the study, which suggests the monoterpene alcohols introduced to beer in the whirlpool are surviving the kettle above their sensory thresholds. 

The temperature of the whirlpool is another factor to experiment with to encourage monoterpene alcohols to find their way into the fermenter. Takako Inui, a Specialist in the Beer Development Department at Suntory Beer Ltd., Japan showed that late hopping at 185°F (85°C) retained slightly more measured linalool compared to late hopping warmer at 203°F (95°C) or cooler at 167°F (75°C). ³⁵ Because of the research (as well as intentionally trying to have less bitterness from significant whirlpool additions) at Sapwood we are generally targeting a whirlpool temperature around 180°F (82°C). 

The biggest reason to focus on these monoterpene alcohols is that they are being tested in significant concentrations in the finished beer and thus are likely to have an impact on final flavors and aromas. Again, it makes sense to focus on hop compounds that are surviving the entire brewing process. Geraniol is the one caveat in that it’s tested in beer pre-fermentation but can decrease during fermentation. The reason is it’s converted (biotransformed) into beta-citronellol (lime-like), which likely a topic worthy of its own post! 

Applying the research suggests that hops high in total oil and high in these oxygen-containing monoterpene alcohols could be good targets for whirlpool flavoring. Hops that fit this mold are Bravo, Brewers Gold, Centennial, Columbus, Ekuanot, Mosaic, and Simcoe. 

Hop-Derived Esters

Moving to another class of compounds that the research suggests is important when trying to be efficient at choosing hot-side hops are hop-derived esters (mainly isobutyric esters). Hop-derived isobutryic esters are found in high levels in dry-hopped beers (their transfer rate has been tested as high as 80%,³⁶ but also from heavily whirlpooled beers. It’s important to note that beers that are only kettle hopped (early bittering addition) have very few of these compounds. The science has found that these isobutric esters likely contribute to the final flavor and aroma of late hopped beer, which is why it’s worth taking a closer look at.³⁷

Isobutyl isobutyrate, isoamyl isobutyrate, and 2-methylbutyl isobutyrate (2MIB) are the three primary studied hop-derived esters in hop-forward beers. Together, these esters have a fruity apple and apricot-like flavors. Of the three, it’s likely of the three esters, 2MIB is the most dominant component. All three of these hop-derived esters have been found to decrease in concentration during wort boiling, suggesting that whirlpooling hops high in these esters is the best way to encourage them to get into the fermenter. 

In a study that looked at hop-derived esters concentrations in final beer from late hopped wort testing 42 different hop varieties (with a dosage rate of just 0.8 grams/liter (~0.25 lbs/bbl)) gives us a good look at which hops might be best used in the whirlpool. I wish the paper used higher late-hopping rates as we typically whirlpool closer to 7 grams/liter (~2 lbs/bbl), which is about nine times greater than the study. It seems logical to conclude that the results below would be increased at the higher hopping rates, likely getting above the threshold. 

Of all of the 42 hops tested, those used for late hopping with the most hop-derived esters from branch-chained alcohols of isobutyl isobutyrate, isoamyl isobutyrate in the finished beer were Nelson Sauvin, Amarillo, and Citra. The hops that tested the highest in the most dominant hop-derived ester 2MIB (in order of highest) Southern Cross, Pacific Jade, Vic Secret, Bravo, and Polaris. Of these, only Southern Cross and Pacific Jade were in concentrations above the threshold (78 ug/L), but the rest were very close. ³⁸ 

How might fermentation and yeast strains impact these hop-derived esters? In a 2020 paper, beers were brewed with Simcoe, Citra, and Mosaic in the whirlpool and tested for final concentrations of the various isobutryic esters across multiple yeast strains and found that SafAle S33 and SafAle K97 retained the highest concentrations (US-05 had the lowest levels) of isobutryic esters.³⁹ None of the yeast strains appeared to produce beers with 2MIB above its threshold. An interesting follow-up would be heavily whirlpool hopping with varieties like Southern Cross or Huell Melon with SafAle S33 or K97. 

It’s possible the reduction in isobutyric esters during fermentation is the result of transesterifications of hop oil esters. In other words, these esters could be biotransformed into other aromatic compounds during fermentation, similar to geraniol converting beta-citronellol. I look forward to learning more about this area! 

If we want to try and push these fruity apricot-like hop-derived esters in our beer, we might want to experiment with hops that have shown to produce beers with higher concentrations and combine them with yeast strains that also test high in the final beer. For example, it might be worth trying out yeast strains such as SafAle 33 or Safale K97 for primary ferment (combined or even copitched with other strains) paired with heavy whirlpool additions with hops like Southern Cross, Pacific Jade, Vic Secret, Bravo, and Polaris (to push 2MIB specifically). 

Hop-Derived Branched-chain Fatty Acids 

Separate from the hop-derived esters looked at above coming from branch-chained alcohols, those coming from branched-chained fatty acids have also been found to be important compounds to keep in mind when considering hot-side hop varieties. During fermentation, hop-derived fatty acids can be esterified into three important esters (ethyl isobutyrate, ethyl isovalerate, and ethyl 2-methybutyrate) that can contribute to the flavor and aroma of beer because of their very low taste thresholds (as seen below). 

Thresholds in Beer:
ethyl isobutyrate: 6.3 ug/L
ethyl 2-methylbutrate: 1.1 ug/L
ethyl isovalerate: 2.0 ug/L 

Where do these fatty acids from hops come from? Age on hops can increase the concentration of fatty acids, as it’s been found that the oxidative-degradation of hop bitter acids results in the formation of branched-chain fatty acids. It’s assumed that hops with higher concentrations of alpha-acids contain higher levels of these fatty acids. 

During fermentation, these fatty acids can be esterified to fruity ethyl esters described above (isobutyl isobutyrate, isoamyl isobutyrate and 2-methylbutyl isobutyrate (2MIB)) through biotransformation. But the acids themselves that remain in the beer might also play a role, mainly through the synergy of the fatty acids with monoterpene alcohols. 

A 2019 paper found that hop-derived fatty acids in beer can strongly enhance the perception and intensity of monoterpene alcohols. Specifically, that paper found (through triangle test with a trained panel) that the addition of 2-methylbutric acid could enhance the “tropical” characteristic of beer and isovaleric acid could increase the “fruity” characterisic of beer. Here the acids were added to a solution designed to mimic a Citra hopped beer in terms of monoterpene alcohol concentrations.⁴⁰

The above paper went on to test 12 different hop varieties for final beer concentrations of these hop-derived fatty acids. Of the hops tested, Apollo and Bravo both tested as some of the highest producers of these two important synergistic fatty acids (2-methylbutric acid and isovaleric). Because these acids can increase during aging, it might be worth whirlpooling with slightly aged Bravo or Apollo when trying to enhance the tropical and fruity characteristic of hot-side saturated flavor through synergy with monoterpene alcohols. 

To ensure I understood the research correctly and to try and get some applicable recommendations from the findings, I reached out to Kiyoshi Takoi, the sole author of the study and he agreed with the idea of experimenting with Apollo and Bravo specifically. Takoi also suggested that when the alpha-acid contents in hops increase, the amounts of these branched-chain fatty acids derived from hops also increase. So, high alpha/super alpha hops could increase the amounts of fatty acids in wort and finished beer.

Knowing that if we slightly age hops (like Bravo and Appollo) to increase the fatty acids, I asked how long and at what temperature brewers should keep them. Takoi suggested that to increase these fatty acids in hops; the storage condition should be 68°F-86°F(20-30°C) for about one year. He also noted that dried whole cone hops might age better than hop pellets for these purposes. Hop pellets should be stored at room temperature under open-air conditions. 

As hard as it might be for brewers to do, it might be worth cutting a few wholes in bags of Apollo or Bravo and leave them at ambient before using them in the whirlpool. However, I wouldn’t throw all your eggs in one basket as it makes sense to me to try and encourage as many diverse sets of hop compounds into the fermenter as possible. Because of this, I’d also pair the aged hops with other varieties mentioned in the study that are high in monoterpene alcohols, thiols, or hop-derived esters.  

Of the hop-derived fatty acids coming from hops, 2-methylbutyric acid has been tested to increase during fermentation, whereas isobutyric acid and isovaleric acid have been found to decrease. A paper looking at 40 different hop varieties and the final concentrations of 2-methylbutyric acid found that beers made with Huell Melon had the highest levels followed by Ekuanot, Apollo, and Polaris. ⁴¹

Before moving on to thiols – to recap the studies so far – whirlpooling hoppy beers with hops high in monoterpene alcohols (like linalool and geraniol) can increase hot-side hop flavor. These can be hop varieties like Bravo, Brewers Gold, Centennial, Columbus, Ekuanot, Mosaic, and Simcoe.  

Hop-derived esters coming from whirlpool hops can impact the final flavor of beer, and hops that have tested on the higher end were Southern Cross, Pacific Jade, Vic Secret, Bravo, and Polaris. Yeast strains can impact the concentrations of the important hop-derived esters, and two strains that may retain them the most are SafAle S33 or K97. 

Hop-derived fatty acids, which are formed on slightly aged hops, can have an important synergistic impact on the important monoterpene alcohols, by amplifying their perception. Slightly aging hops can increase these fatty acids. Hop-derived fatty acids can also impact beer if they are esterified during fermentation into fruity, low threshold esters. 

Polyfunctional Thiols 

Polyfunctional thiols are the portion of a hop’s sulfur compounds that can be desirable in beer because of their potential for intense fruity flavors. 

The main thiols studied in hops (and in wines) are 3-mercaptohexanol (3MH), 4-mercapto-4-methylpentan-2-one (4MMP) and 3-mercaptohexyl acetate (3MHA), which is converted from 3MH.  

4MMP has a blackcurrant and catty aroma (at high concentrations). Taste threshold 1.5 ng/L
3MH has a grapefruit/rhubarb flavor. Taste threshold 55 ng/L.
3MHA has a passionfruit flavor. Taste threshold 4 ng/L.⁴²

Focusing on how these fruity hop-derived thiols are impacted by the boil, a study tested thiol levels throughout a boil using Simcoe. The authors found that during a 60-minute boil at 212ºF (100°C), 4MMP content decreased 91% and 23% after heating to just 194ºF (90°C). On the other hand, 3MH increased threefold at 212ºF (100°C) than at 90ºF (32°C), which suggests that not only is this fruity thiol preserved during the boil but enhanced! 

When it comes to trying to push hot-side saturated hot flavor, it makes sense to pay closer attention to the 3MH levels of hops and potentially use them in the whirlpool and even for bittering. If you are trying to push 4MMP levels, late hopping at cooler temperatures is likely best to encourage the thiol to get into the fermenter. 

Again, synergy appears to be an important part of why these fruity thiols are important hot-side compounds. A paper put 4MMP (blackcurrant) thiol to the test with monoterpene alcohols (linalool, geraniol, and β-citronellol). The results showed that 4MMP did have an additive impact with monoterpene alcohols and that only 1.2 ng/L was needed for this effect to occur (which is close to it’s threshold value). Specifically, the synergy between 4MMP and linalool, geraniol, and β-citronellol enhanced tropical characteristics. Using hops rich in both 4MMP and monoterpene alcohols could result in a more perceived intense tropical flavor. This process is similar to how the hop-derived fatty acids above intensified monoterpene alcohols, showing how complex hot-side hop flavor can be! 

Survivables

I did my best above to layout what hot-side compounds might be contributing the most to fruity flavors in beer (monoterpene alcohols, hop-derived esters and acids, and thiols). Whether it’s through synergy or being in the beer above a sensory threshold, the compounds above are being tested to be in packaged beer and key drivers to hot-side hop flavor. 

Finally, this brings us to the most recent research in this area from Yakima Chief Hops. If we know what compounds are likely the most important to hot-side flavor, why not test which hops have the highest combination of all these compounds? This is exactly what Yakima Chief did and coined these compounds as “survivables.” I like it! 

Below are the results of Yakima Chief’s study⁴³ (and one of the more exciting hop charts I’ve seen in a while). Testing hops for a combination of monoterpene alcohols (linalool and geraniol), thiols (3MH), and hop-derived ester (2MIB), you can see why I was likely so bullish on Idaho 7! Idaho 7 leads the pack when it comes to having the most of these survivable compounds and why it’s likely such a great hot-side hop. Not far behind are Mosaic, Bravo, Citra, and Millennium, Mount Hood, Euaknot, and Simcoe. Yakima Chief is using the research to put together a blend of Cryo called TRI-2304CR, that will be a blend of hops that are loaded with these survivables! You can check out the full presentation on their webinars website. 

Conclusion

Hopefully, this post helps inspire some new experimentation when it comes to packing in as much hot-side hop flavor as possible into your beers! 

Below is a list of the hops that came up in the research that may be great to play with in the whirlpool. Because hot-side flavor is so complex, it makes sense to try and blend these varieties to push as much sensory explosion as possible! I’m curious to hear which hop, or combination of hops, you have the most luck with to push pre-dry-hop flavor. 

• Idaho 7
• Bravo
• Brewers Gold
• Centennial
• Citra
• Columbus 
• Ekuanot
• Mosaic
• Simcoe
• Southern Cross
• Pacific Jade
• Vic Secret
• Polaris 
• Huell Melon
• Millennium
• Mount Hood
  

Key Points 

• Sampling your beer pre-dry hop is one of the best ways to determine how well your hot-side hops performed. I try to make this a habit.  
• Monoterpene alcohols like linalool and geraniol are consistently mentioned as key components of determining hop flavor intensity. To push hop-derived monoterpene alcohols in beer, lowering the temperature of the whirlpool to 185°F (85°C) may be worth exploring. 
• Hop-derived esters help to give beer fruity apple and apricot-like flavors and are likely retained at higher concentrations when added to the whirlpool. 
• Hop-derived fatty acids can impact the flavor and aroma of beer through the esterification processes (which have low thresholds) and synergy. Specifically, the acids can amplify the sensory experience of monoterpene alcohols. 
• Slightly aging your hops (especially Bravo and Apollo) and using them in a blend with other great hot-side hops may be a good way to build in hot-side flavor complexity. 
• Hop-derived thiols have low sensory thresholds, but can contribute to hop fruity hop flavor synergistically and on their own. 
• The thiol 3MH (grapefruit-like) can increase during the boil, but 4MMP is likely retained in higher concentrations during cooler whirlpool conditions.  
• Hops high in a combination of all these “survivables” may be some of the best to experiment with in the whirlpool. 

Bio–T Cryo® Blend hot-side with freeze-dried mango during active fermentation to push fruity flavors.

H

ot-side hop saturated flavor is an essential part of a great hazy IPA. Loading up an IPA with a massive charge of dry-hops alone doesn’t seem to be enough. These types of hazy IPAs lacking in hot-side flavor often come across as vegetal and flabby on the palate. The hop-derived “fruitiness” from the whirlpool helps to carry the dry-hopping. I’ve experimented with zero hot-side hops in the past, and the results weren’t great. 

In this beer, I used a new experimental Cryo Hops® biotransformation blend (Bio-T) in the whirlpool, freeze-dried mango in primary, and 100% Citra dry-hopping post-fermentation all to try and push the perceived fruitiness to the max! 

The base recipe for this is one of my favorites from Sapwood called Rings of Light (a 100% Citra session hazy pale ale). Mike has also blogged in more detail about the beer. On day two of fermentation in the 10 bbl tank I transferred out ~16-gallons into a fermenter with 2 pounds of freeze-dried mangos. Freeze-dried fruit is nice to consider because unlike dehydrated fruit where heat removes or alters some of the fresh fruit flavors, the freeze-drying process is supposed to retain more of these flavors and compounds. 

Because water is removed from freeze-dried fruit leaving behind its sugar content, using it in beer will typically increase your gravity. This is different from using fresh fruit because the water in the fruit will dilute the sugar content. Generally, most fresh fruit additions have a gravity of around 1.050, and the freeze-dried version of that same fruit will have a higher gravity. 

As it relates to freeze-dried mango, one producer’s site claims that .5 ounces of freeze-dried mangos are equivalent to 12 ounces of fresh mangos (x24). If this is the case, then in this beer, the 2 pounds of freeze-dried mangos (in ~16 gallons of beer) is closer to 48 pounds of fresh mangos (or about 3.2 pounds of fruit per gallon)! Another source says that mangos are 83% water, so perhaps a more accurate figure is to assume that we can take the freeze-dried amount used x17. For this beer, we’d be around 2.26 pounds of actual fruit per gallon of beer (271 grams/liter).

To calculate the increased gravity from coming from the fruit, I did the following: 

• 10 grams of freeze-dried mangos = 6 grams of sugar
• 907 grams (2 pounds)/10 = 90 servings (544 grams of sugar added). 
• 1.060 SG to ~1.071 Using the chaptalization calculator

Two days after adding the freeze-dried mango (three days after the start of the base fermentation, gravity at 1.039), there was a clear difference in aroma at this point from the base batch. Despite both being a little “worty.” The mango was cleaner and brighter with a candied fruit aroma (circus peanuts, peachiOs, lucky charms marshmallow thing). Rings of Light from the 10bbl tank was still somewhat fruity, however. 

Bio–T Cryo® Blend.

I paid particular attention to the flavor of the base beer before dry hopping because of the use of a new product sent to us to try out from Yakima Chief called Bio-T Cryo® Blend. It’s Yakima Chief’s first time blending varieties into Cryo® pellets. The theory behind Bio-T is to create a blend that loaded in “survivables” (geraniol, linalool, 3MH, etc.). 

Looking a little closer at the Bio-T Cryo® Blend hop oil makeup, you can see it’s not crazy high in any one particular compound. Running it through a hop database calculator I’ve created to try and get a sense of new hop varieties, the overall figures most closely resembles Cascade, but with a more Centennial-like geraniol content. However, this is comparing Cryo® to T-90 hop pellets, the higher total oil in Cryo® would translate to more of those oils finding it’s way into the wort. The downside of using Cryo® on the hot-side is the higher alpha-acid content which can bring up the IBUs and increase the bitterness a little too much. I would typically add more hops to the whirlpool in this beer, but had to back down for this reason. 

If some of Yakima Cheif’s Cascade Cryo® is being used in this blend I wouldn’t complain because I think it’s a prtty good hot-side hop. Cascade has a has a relatively low amount of free compounds and an extremely high amount of bound compounds that need to be released during fermentation (particularly 3MH precursors).⁴¹ One theory is that hops high in bound thiol precursors should be added during the late hopping phase to help cleave these precursors during fermentation. On the other hand, hops that are rich in free thiols can be added to the dry hop where enzyme activity from yeast isn’t required to release the aromatic compounds. Other hop varieties high in bound the 3MH thiol are Calypso, Saaz, and Hallertau, which might also be great late-hoping choices to try and utilize the most of the hop through fermentation.⁴⁴

The liberation of bound thiols is done via an enzyme called β-lyase produced by yeast. Most yeast that have tested positive for β-lyase are not typical ale strains, but wine strains, which isn’t to say that typical ale strains don’t produce the enzyme, but they just haven’t been tested yet. Looking back, I probably should have considered adding a commercial enzyme to this beer during fermentation to try and push the release of 3MH (if Cascade is being used in the trial blend) as well as release any bound compounds that might still be available on the freeze-dried fruit. One such product is called Rapidase Revelation Aroma, which is designed for extraction of aroma precursors, typically thiols for white grapes, but theoretically could extract the same thiols in hops and other fruits. I would start experimenting with a dosage of 0.5 to 1 gram per 5-10 gallons of Rapidase Revelation Aroma.  

Recipe

Brewed: May 2020
Tasting notes: May 2020
Batch size: 5.5-gallon 

Results

I was pleased with how this beer turned out considering it was an experimental batch testing out a new concept! The 100% Citra dry hop is dominating the aroma (which isn’t a bad thing). The mango fruit character is there, but it’s a light touch (I can pick it out most on the back end). If I didn’t know fruit was added during primary, I’m not sure I’d even pick it out, it’s kind of masked by what I would consider hop-flavor. On the other hand, if you tell somebody fruit was added, I don’t think they would have a hard time believing you. 

Regarding the Cryo Hops® Bio-T blend, it’s hard to determine how much the blend is adding to the beer without doing direct side-by-sides. However, tasting the base beer (without the fruit) before dry hopping, I did get a pleasant orange/tangerine aroma. Without sending a beer to a lab to get tested for final hop compounds, it’s impossible to say how much biotransformation is taking place due to the makeup of oils of the blend. I do wish it was slightly lower in alpha-acids so I could load up the whirlpool with even more hops to try and push as many hop compounds as possible into the fermenter without picking up too much bitterness. 

I think the addition of the freeze-dried fruit helps to brighten up the beer compared to the base. For what it’s worth, I could pick out the mango much more before dry hopping suggesting the dry hops are masking the aroma a bit. When it comes to adding fruit during active fermentation, much like with adding dry hops during fermentation, many of the aromatic compounds can be scrubbed so I’m not surprised it’s not super mango-forward. In this case, the addition helps to make the beer more layered and complex without taking over completely. 

The downside of using freeze-dried fruit during active-fermentation like this is there doesn’t seem to be a great way to sanitize it. This isn’t a problem for the most part, especially if you keep the beer cold after packaging and drink relatively quickly. However, I’d be nervous about doing a big canning run at the brewery using this method. With this batch in mind, we plan to use freeze-dried mango powder in the whirlpool in an upcoming fruited DIPA collaboration with Great Notion. Here, the whirlpool temperature should help sanitize the powder and hopefully give us a good hop/fruity saturated foundation to accompany more fruit and hops on the cold-side! 

We sent a few mini-crowlers (16 ounce cans) of this beer out into the wild if you’re interested to see what people other than myself thought of this little experiment on Untapped!

Cashmere IPA 

Fermented with Conan and Hefeweizen Yeast

O

ne of my favorite things to do at the brewery is experiment with small batches. Sometimes I’ll transfer 5-gallons of fermented hoppy wort pre-dry hop to a purged keg with experimental hops. Other times I’ll take a little wort pre-ferment to test out different yeast strains or blends; we just got a small 18-gallon conical to make this type of experimentation a little easier and more representative of brewing something on the bigger tanks. 

This particular experiment is a built in part on yeast blend beer that we’ve done in the past at Sapwood combining hefeweizen yeast with RVA Manchester and active fermentation dry hops with Cashmere (only this time I used a Conan strain). The slight vanilla yeast characteristic you get with RVA Manchester combined with approximately 10% hefeweizen yeast lends an approachable vanilla wafer-like beer. The active fermentation dry-hopping helps to create a baseline hop-fruit character but with most of the volatile green compounds blown off with the CO2 produced during fermentation. After drinking a beer from Tree House called Cachet (a DIPA w/ Cashmere dry hops), we were inspired to do a more grown-up version of our RVA/hefeweizen yeast blend beer. So, we upped the basemalt to get into DIPA territory (for a starting gravity anyways) and dry hopped it with 100% Cashmere at a high rate of 12 ounces per 5.5 gallons (~16 grams/liter). 

I took approximately 5.5 gallons from an active fermenting 20 bbl tank (about 24 hours post-pitch) with a Conan strain and added 5 grams of WLP300 from a vial. I still want the fruity ester profile you can get with Conan, but with a banana hefe-edge while attempting to keep any clove flavors to a minimum. I fermented the mix-pitch relatively cool, starting at 65°F (18°C) and allowed it to finish off closer to 70°F (21°C). I dry hopped in two stages, the first with 6 ounces (170 grams) at the tail end of fermentation in primary and again with 6 ounces (170) grams in a purged keg (with a dip tube filter). After three days in the keg, I transferred out into a serving keg where it sat on CO2 to carbonate. Because of the intense dry-hopping rate, this beer needed close to two weeks in the serving keg to settle down. After the green hop bite died down, we had the beer on tap for a few days for us to try then eventually filled 16-ounces mini crowlers and sent 18 cans out into the world. People liked it a lot, much more than I thought they would (spoiler alert, people like sweet things!).  

Recipe

Brewed: March 2020
Tasting notes: April 2020
Batch size: 5.5-gallon 

Results

To say this beer is sweet is an understatement; it’s not rare for imperial stouts to finish this high (or much higher), but for an IPA this one is up there! Surprisingly, because of the high dry hopping and hefeweizen yeast, the result isn’t “worty,” but more of a dessert-cookie maltiness. This is in the category of a dessert IPA for sure, especially considering if you down one 16-ounce can you’re also taking down 400 calories (but who’s counting). It’s got a super soft mouthfeel, with a cloying lingering sweetness. 

If you like Banana runts, then you will love this beer. Once that descriptor was used, I couldn’t shake it. It’s one big banana runt bomb! Buried in this is also faint vanilla wafer, lemon poppy-seed, melon, and coconut flavors. With just a small pitch of WLP300 (after fermentation was underway) it still has plenty of banana! I’m always amazed at how little a pitch of a different strain can drastically change the fermentation profile of a beer. 

Overall, it’s a fun beer. I’m not sure we’ll ever considering scaling this up, but for 5-gallon it was fun to have on tap for a few days. I’d probably mash a little lower next time and try to get that FG a little lower, considering this is generally a good starting gravity for a DIPA. My guess is that anyone replicating this recipe will get a lower FG and if you want to bump it up, you could consider boiling maltodextrin and filtered water and jumping from keg-to-keg to build up the FG. I’m still a little unclear why it finished so high, but sometimes it’s fun to brew something unique and out of character! Runt up!