The Food Programme is a well-known and respected weekly look at all things food here in the UK. I personally think they did a really good job of the programme.

You can listen to it on the BBC’s iPlayer here.

As the iPlayer content is refreshed regularly if you’re reading this post some time after posting you should still be able to download a podcast of the programme here.

I hope you enjoy it.

Calling all brewers!

We’d like to ask for your help. We’re carrying out a survey relating to the use of yeast food in breweries. This forms part of a project being carried out in our laboratories this summer by a visiting intern from France – Charlène Gosseaume.

Charlène is working on a project which is looking to understand what proportion of brewers use yeast foods, the reasons why they use them, the circumstances in which they make use of them, and what sorts of products prove most effective.

The survey she’s carrying our complements some laboratory work we’re currently undertaking to better understand the contribution of yeast foods to wort nutrition.

We would really appreciate it if you would take a few moments (3 – 6 minutes to be more exact) to take our survey. Whether or not you currently use yeast foods (including zinc salts, or any fermentation supplement) we’d welcome your input.

The survey is anonymous, unless you chose otherwise – if you give us your email at the end of the survey we’ll give you access to the survey results when they’re complete.

The survey can be found here.

Please spread the word to any and all commercial brewers you know. The more responses we have the better.

Thanks!

Many of these are destined to be repeated across other breweries within the brewery’s parent group costing a huge amount of money over the long term.

Tools and techniques

A variety of tools can be put to use to resolve production problems encountered in breweries. These generally aim to break down the problem solving process into its component parts

• Firstly an incident (a single incidence of a problem) is identified from its symptoms. Our aim is to define what’s gone wrong (the ‘fault’, ‘problem situation’ or ‘non-conformance’) and capture the what, when and where relating to the incident.
• Next we look to define the problem. At this point we want to understand why the problem is important (including understanding the financial and non-financial implications of the problem), have a clear idea what is and what’s not wrong, understand how urgently we need to find a solution to the problem, and understand potential root causes. From the root causes we’ll develop an appreciation of any co-symptoms that we might expect to see.
• Next data is collected to help discriminate different possible root causes of the problems. The key here is to capture all the symptoms associated with this incidence of the problem as an aid to future diagnosis.
• The data are then critically evaluated to allow as many possible root causes to be eliminated.  Further data or experimental trials may be needed to reduce numerous possible root causes to one possibility and thus diagnose the true root cause. Where we are trying to get to is to have the who, what, when, and where of the problem – we need to identify the ‘point of cause‘ (the ‘smoking gun’).
• Having identified the root cause the next step is to identify a range of possible solutions that can be used to eliminate the root cause.
• Various tools can then be applied to analyse the strengths, weaknesses and inherent risks in implementation of the different potential solutions.
• One or more solutions are then chosen and implemented with the aim of achieving incident closure. At that time plans for following up on the incident to ensure that the underlying cause has been eliminated are also put into place.
• On-going monitoring and reporting are used to ensure that no re-occurrence of the problem takes place. The problem solving process is never finished until we are sure that the problem has gone away and is unlikely to ever appear again. Unfortunately, this key step is often missed out from many brewery problem-solving initiatives.

This overall problem solving methodology can be used in different formats. For minor problems which need to be dealt with quickly (for example by implementation of a workaround) the process shown opposite is often effective.

This type of problem solving process can be carried out either by an individual or by a small team comprising no more than two or three people. Some brewing companies use problem solving tools, such as ‘5 whys’ as an aid to such short-form problem-solving processes.

Dealing with more complex problems

More complex problems require more complex methodologies and the input of more people. Brewery problems are often open problems, that is they have more than one contributory cause (and therefore multiple potential solutions), rather than closed problems, which have only one cause (and therefore one solution). Thus many useful but nevertheless simplistic methods which are highly valued in other industries are of less use in the complex mix of biology, chemistry, physics, engineering and psychology which is the brewing process.

The diagram below shows the methodology which we have been using within brewing companies for more than a decade with good results. We have applied this method to solving a variety of process problems, including beer off-flavour problems, beer taint problems, beer haze problems, beer foam problems, beer flavour stability problems, brewhouse extract yield problems, yeast viability problems, attenuation problems, filtration throughput problems and packaging efficiency problems.

In our experience methods like this are best deployed with teams of 4 – 10 people. At the top end of the problem solving ‘tree’ are various Six Sigma techniques, including DMAIC (which stands for Define – Measure – Analyse – Improve – Control). Such techniques are ideal for application to larger infrastructural problems within brewing companies.

These problem solving frameworks come to life through the use of specific tools, including Force-Field Analysis, Ishikawa Diagrams, Inverse Brainstorming, De Bono’s Six Thinking Hats and Failure Mode and Effects Analysis. Using these tools isn’t instinctive - training in their use is needed to get the best out of them.

Sharing of information about problems in breweries and how they have been resolved has historically been inadequate. To an extent this has resulted from a lack of tools to facilitate sharing of information about brewery problems and solutions, rather than from a brewery’s resistance to making their problems more widely known within their peer group.

A further obstacle to efficient problem solving has been availability of information, know-how and expertise. By way of example, consider that more than 350 individual faults can occur in packaged beer.

Each of these faults may have, on average, 10 possible root causes. For each possible root causes there might be, on average, 20 or more viable solutions which could be used to eliminate the problem.

Multiplied together this gives us a staggering 70,000 potential solutions to the problems that might occur in a modern brewery. It is little wonder that no single member of staff is capable of dealing with all potential problems in an efficient way.

Thankfully, the reality is that there are only so many ways for us to damage product quality, product safety, or process efficiency in a brewery so the picture is not quite as complex as I have painted it. Nevertheless it is a knowledge management task which brewers underestimate at their peril.

To understand the importance of efficient problem management in a modern brewery it is useful to consider the typical numbers of problems that arise in a given time in relation to bright beer and packaged beer. Benchmarking studies carried out with five breweries (average size of about 2M hl per year) representing three brewery groups have revealed a preference for categorizing problems with respect to accountability. This can be a useful thing to do. It helps spread the load. But it carries a risk. Most big problems in breweries start out as little ones. The high SO2 concentration that suddenly stops you being able to sell your product without breaking the law might have started out several months ago as a very small problem in the raking of your lauter bed.

In our company we spend a lot of our time dealing with ‘fires’ that have got out of hand in breweries. All of them start as little ‘sparks’ that either no-one noticed, or were thought to be unimportant.

What sorts of problems have you seen in breweries? Which are most difficult to completely eliminate? What could we breweries be doing better in this area?

If there’s one thing to remember, when it comes to brewery problems always expect the unexpected. Face up to the fact that your brewery is going to run into problems – ignoring them is not going to make them go away. You have the potential to increase your profitability dramatically if you can get on top of, and eliminate, your five most important problems. What are you waiting for?

Despite its blindingly obvious importance to the brewing industry there appears to be little original literature in this area.

Work in Japan (Nagao et al, 1999) has drawn a connection between beer drinkability and gastric emptying. Beer quality attributes (such as off-flavours and tainst) which are perceived by consumers to be negative seem to restrict gastric emptying, minimizing the frequency and volume of urination. This has consequential effects on subsequent beer intake. You drink less when you ‘need to go’. A series of very good papers has been published on this area by this research group.

Guinard et al (1998) have explored the relationship between beer composition and the thirst quenching characteristics of beer. While the ‘thirst quenching’ characteristic is an important aspect of drinkability, our understanding of it remains very incomplete.

An attempt to evaluate differences in drinkability of beers and establish some of the drivers of this parameter has been reported by Parker and Murray (2003) and the area has been reviewed by Sharpe et al (2003) and Mattos and Moretti (2005). A symposium on drinkability of beer was also held in Scotland in late 2006 and a proceedings book published.

If I was to summarize all of this past work in one line – more questions than answers.

The relationship between beer freshness (aging) and drinkability is interesting. Many (including me) believe that stale beers (particularly lagers) are considerably less drinkable than fresh ones. While there are no doubt many reasons for this, the different mouthfeel characteristics of stale beer compared to fresh beer would seem to be important. From a chemical perspective, oxidation of polyphenols leading to a mouthcoating astringency, and formation of compounds such as 2-furfuryl ethyl ether in complex reactions may be important.

Drinkability for Dummies

1.  Drinkability is a real phenomenon, not an abstract construct.

2.  Some beers are more drinkable than others. Leaving aside that it’s easier to work your way through six pints of 4% bitter than the same volume of 9.5% barley wine, the issue is that two beers of nominally the same alcoholic strength, bitterness and beer style can have markedly different drinkabilities. Big enough to cost you and all your colleagues your job if you work for the brewery that makes the less drinkable one.

3.  If you are trying to make a brand that needs volume for success, you either need a lot of customers or good product drinkability. Duh!

4.  Science has provided us with tools to understand this area – we just need to apply them.

The Top 10 Questions of Beer Drinkability

Questions that remain to be answered include:

1.  What is drinkability? What is it not? How do drinkability and satiety relate to one another?

2.  Does drinkability arise from a conscious process, or as a result of unconscious brain activity?

3.  How does beer composition affect drinkability? Is beer drinkability more about the absence of negatives, or the presence of positives? Some believe it’s all about making the beer ‘clean’ – not everyone agrees.

4.  Which is more important as a driver of drinkability – appearance or flavour? Some say we ‘drink with our eyes’ – the first few gulps maybe, after that taste does matter.

5.  Is product consistency a good or bad thing for drinkability? Does consistency lead to product boredom? In other words, can you have too much of a good thing? Most large brewers, and many smaller enterprises strive for product consistency. Some would argue that the more consistent some brewers products have become the less beer they have sold. Have they thrown the baby out with the bathwater?

6.  How might drinkability be measured? Many of the big brewers seem to be scared stiff of this area, worrying that anything they do might be seen as indirectly encouraging ‘binge drinking’ or get associated with other ‘health and safety’-related bad press. They may be right.

7.  What is the relative importance of sensory aspects and physiological aspects to drinkability?, ie if salts content of beer is an important driver of drinkability do the salts exert their effects by a physiological route, or via a sensory psychology route?

8.  What types of beer are most drinkable? What things do they have in common?

9.  What types of beer are least drinkable? What things do they have in common?

10. Perhaps the biggest question of all – why aren’t brewers falling over themselves to get to the bottom of all of this?

What are your views on the drinkability of beer? What makes a drinkable beer? How can you go about designing and making a drinkable beer?

Further reading (of the scientific literature kind)

Guinard JX, Souchard A, Picot M, Rogeaux M, Sieffermann JM (1998) ‘Determinants of the thirst-quenching character of beer’. Appetite. 31(1):101-115

Mattos R and Moretti RH (2005) ‘Beer drinkability – a review’. MBAA Tech Quarterly 42, 12-15.

Nagao Y, Kodama H, Yamaguchi T, Yonezawa T, Taguchi A, Fujino S, Morimoto K and Fushiki T (1999), ‘Reduced urination rate while drinking beer with an unpleasant taste and off-flavor’, Bioscience Biotechnology and Biochemistry, 63, 468-473.

Parker D K and Murray J (2003), ‘The different roles of consumer and expert panels’, in Proceedings of the European Brewery Convention, Dublin, Nurnberg, Ferlach Hans Carl, 814-821.

Sharpe, R, Pawlowsky K and Chandra S (2003), ‘Drinkability and drinkability mapping’, in Institute and Guild of Brewing Africa Section, Proceedings of the 9^th Brewing Convention, Victoria Falls, Zambia, South Africa, IGB Africa Section, 58-64.

Definitions

Yeast growth

Although we tend to use the term ‘yeast growth’ we should really discriminate two different things:

• Increase in cell biomass
• Increase in cell numbers

It’s important to notice that word increase. In other words it all depends on what you start with. What goes in must come out – and then some!

In a well-managed brewery fermentation yeast growth is synchronous – that is, the cells all bud at once. Under these conditions we will get twice as many cells as when we started, four times as many or eight times as many, but not any multiples in between.

Growth of brewer’s yeast by budding

Thus, if you think your yeast is multiplying to say three times its original weight (rather than two or four times), there are several possibilities:

• You have not accounted for all the yeast in the system
• Your fermenter contents are not homogeneous (this is termed fermenter stratification)
• You have pitched your yeast into the fermenter at different times, which means it has started and stopped growing at different times
• You are not using a pure yeast culture
• A significant proportion of your original cells were dead, or unable to reproduce under the conditions in the fermenter

In the case of biomass however, a much wider range of ‘growth’ is possible, since the individual cells can be bigger or small than ‘usual’ or can be fatter or thinner than ‘usual’.

Biomass

• Biomass is the weight of cell mass – we can express it on a dry basis, wet basis, or on a standardized slurry basis (eg 60% solids).
• The total biomass produced is calculated by subtracting the final biomass from the inoculated biomass.
• The new biomass produced is of interest as this is what results in ‘lost’ extract – wort carbohydrates, amino acids and lipids which are consumed by the yeast and converted into new cells. This is the difference between the final quantity of yeast produced in the fermenter and the amount of yeast pitched. To make this comparison it is important that the cells are in exactly the same physiological state at the time they are quantified.

Yeast growth in the brewery

For a given pitching rate, the amount of yeast that is cropped from the fermenter is affected by a number of key variables. These include:

• The pitching rate
• The yeast viability
• The yeast strain
• The purity of the yeast culture
• The wort composition
• The particulate content of the wort
• The timing and extent of wort aeration / oxygenation
• The fermentation conditions

Growth measures

The number of doubling (budding) events (n) can be calculated from the following equation:

n = 3.32 log₁₀ (X/X_o), where X = the final cell number and X_o is the initial cell number

Biomass can be substituted for cell number in this equation, but this gives rise to a risk of estimation errors. More typically, brewers will estimate the ‘growth’ of yeast by comparing yeast biomass before and after fermentation. Because we harvest what we pitch, what really matters from a beer loss perspective is how much new cell biomass has been synthesized.

For example:

• Suppose we pitch a 4,000 hl fermenter with 2,500 kg yeast slurry at 60% solids. This is equivalent to 1,500 kg of solid (wet) yeast.
• Let’s assume that at the end of fermentation we harvest 9,000 kg yeast slurry at 60% solids. This is equivalent to 5,400 kg solid (wet yeast).
• Furthermore, let’s assume we collect about 250 kg of ‘scrappings’ at 40% solid – equivalent to 100 kg of solid (wet) yeast.
• And, from the yeast of the remaining beer we estimate that it contains the equivalent of a further 800 kg at 60% solids – 480 kg solid (wet yeast).

So we started with 1,500 kg of solid (wet) yeast and ended up with 5,980 kg of solid (wet yeast).

The number of doubling (budding) events (n) can be calculated from the following equation:

n = 3.32 log₁₀ (5890 kg/1500 kg)

This gives a value of 1.92 budding events.

Two budding events of 1,500 kg of yeast should give a total of 6,000 kg of yeast, comprised of 4,500 kg of ‘new’ yeast and 1,500 kg of original yeast. This ‘theoretical’ figure of 6,000 kg is very close to the 5,980 kg in this example.

The wet (compressed) weight of brewing yeast is typically five times its dry weight. Thus 8.3 kg of slurry yeast (at 60% consistency) is equivalent to 5 kg of solid (wet) yeast, which is equivalent to 1 kg of dried yeast.

Growth limitations

What limits the growth of yeast in brewery fermentations? Much depends on the relative quantities of key nutrients.

• Growth of yeast in some fermentations is oxygen limited.
• In others it is nitrogen (amino acid) limited.
• Minerals, such as zinc, can sometimes be limiting.
• In very bright worts, fatty acids and sterols can be limiting.
• Inhibitory substances such as dissolved carbon dioxide can also affect both growth extent and growth rate.
• Very occasionally, the concentration of specific vitamins or co-factors can be limiting.

Influence of pitching rate

The relationship between pitching rate and total new biomass formed is non-linear.

• At low pitching rates the amount of new biomass formed is low – as the pitching rate is increased the amount of new biomass increases.
• At high pitching rates, growth is suppressed and the amount of new biomass formed is low again.

One way to think of this is that at low pitching rates, most nutrients are in excess – there is plenty to go round. But at high pitching rates, most nutrients are in short supply. It’s a bit like sharing food at a party – few guests, lots of food for everyone; many guests, not enough food for everyone.

Putting it all into practice

If you want to produce a flavour-neutral beer, with moderate concentrations of yeast-growth-related flavour compounds, you should target formation of a moderate amount of new biomass.

• For a pitching rate at high gravity of about 15 x 10⁶ cells / ml two budding events will be enough – this will give a peak yeast count of 60 x 10⁶ cells / ml.
• The fermentation rate will be moderate – not too fast, not too slow, assuming a primary fermentation temperature of about 12^oC.
• This will be associated with production of a moderate amount of glycerol (about 2.5 g/litre) – about average from an extract loss perspective, and a fair balance with beer quality.

If you want to produce the beer in a different way you have two options – low pitching rate or high pitching rate.

Option #1

• For a pitching rate at high gravity of about 5 x 10⁶ cells / ml four budding events will give a peak yeast count of 80 x 10⁶ cells / ml.
• Provided the initial fermentation temperature is higher – say 14 – 16^oC the fermentation rate will be sufficient.
• This will be associated with production of a high amount of 4.14 g glycerol per litre of high gravity beer – by no means perfect not perfect from an extract loss perspective, but a fair balance with beer quality – this beer will be more flavoursome.

Option #2

• For a pitching rate at high gravity of about 35 x 10⁶ cells / ml one budding events will give a peak yeast count of 70 x 10⁶ cells / ml.
• The high initial yeast count will allow lower fermentation temperatures to be used, say 8 – 12^oC.
• This will be associated with production of a 1.94 g of glycerol per litre of high gravity beer – pretty good from an extract loss perspective, but higher than produced in the original example above. This beer will be less flavoursome.

One gram of dry yeast typically contains 1,000 million cells (10¹⁰ cells). So if you pitch 1 gram of dry yeast into a litre of wort you’ll get 10 million cells per ml. This is the equivalent of pitching 0.83 kg per hl at 60% solids. Of course, the actual number of cells varies with yeast strain, fermentation conditions, wort etc – but the approximation can be useful.

Extract losses associated with yeast growth in brewery fermentations

There are two main sources of extract loss associated with growth of yeast in brewery fermentation – direct and indirect

• Direct extract losses result from the yeast using wort components (carbohydrates and amino acids) either for (i) growth or (ii) maintenance of cell function – by manipulating the fermentation conditions we can control these losses but we have to watch out for effects on both beer quality and yeast health. Push these losses down too far and you will get bad beer and sick yeast. Some of these direct extract losses can be temporarily ‘borrowed’ from and ‘paid back’ to the yeast. For example if yeast which is high in glycogen is pitched into the fermenter but that yeast is then left on the beer for a while at the end of fermentation, the yeast will ferment the glycogen and give us some ‘free’ alcohol.
• Indirect extract losses result from entrainment of beer within yeast which is removed from the fermenter. Some of these indirect losses get recycled when we re-pitch the yeast. The more yeast we throw away, the higher this source of loss. The thinner the yeast, the higher will be this loss.

Summary of factors which affect yeast growth in a brewery fermentation

The following parameters affect the growth of yeast in a brewery fermentation. Whether a factor is limiting or not will be influenced by the yeast strain, the pitching rate, and fermentation conditions such as fermentation temperature, fermenter shape etc.

Supply of brewing yeast cultures to breweries within a multi-site brewery group presents many challenges. The objective is to make sure that all breweries within your group are using the right yeast strains, in the best possible condition, with the lowest possible risk of failure. If multiple strains are supplied within a group (different lager strains, ale strains, wheat beer strains, or yeasts for production of low alcohol beers for example) it is important that potential mix-ups are anticipated and actively prevented.

Whether the yeast supply function is in-sourced within your head office laboratory or out-sourced to a specialist organization like Cara Technology, the challenges remain the same.

Here, we explain what’s involved in doing this right, and offer some pointers to drive continuous improvement in this area.

Yeast strain provenance

You need to be able to demonstrate the origins of your yeast cultures, assure traceability, and be sure as a business that your yeast strains are fit for purpose.

First of all, the origins of all your yeast strains should be known and traceable. That means it should be possible to run an audit trail from your currently-used brewery yeast culture right back to the culture which was isolated within your laboratories, or obtained from a third party – whether that was yesterday or may decades ago.

While it may well be that the particular yeast used in your breweries has been selected for historical reasons, it is usually preferable to select the strain on the basis of its possession of a number of desirable traits, and the absence of undesirable traits.

For example, for making a modern pale lager beer in upright cylindro-conical fermenters the following traits are ideal:

• Pure culture of a single genetic type
• Mitochondrial mutants (including respiratory-deficient variants) present at <2% of the total
• High degree of attenuation
• Low requirement for free amino nitrogen (amino acids)
• Reliable flocculation properties of a type suited to the fermenter shape and size in use in your breweries
• Good ability to reduce diacetyl to acceptable concentrations in an acceptable time
• Good flavour production with respect to esters and higher alcohols
• Low production of volatile sulphur compounds
• Good (though not excessive) production of sulphur dioxide – for a long flavour life

The genetic background of the strain should be proven and verifiable – for example, you should be able to demonstrate that your yeast has not been genetically modified.

Yeast strain identity and purity

Genetic tests, phenotypic tests, checks for contaminant microorganisms, with the performance of all test methods regularly validated

Having established what is required for success it is important that methods are put in place to make sure that what is intended has been acheived. Genetic tests of identity and purity can be carried out using PCR-based DNA fingerprinting or by karyotyping. Phenotypic testing – for example, tests for flocculation, fermentation performance, and the presence of certain traits, such as the ability to grow at different temperatures, possession of certain enzymes, or the ability to grow in the presence of specific antimicrobial agents – are also useful.

Tests for the presence of contaminant microorganisms (wild yeasts and bacteria) must also be carried out.

Finally, all of the laboratory tests have to perform as intended. You can’t know they do unless you check them. All methods should be validated at frequent intervals to assure performance.

Yeast strain preservation

Cryopreservation of master cultures, two geographically-independent secure sites – well-entrenched ISO, HACCP and disaster recovery systems

The preservation technique used is critical. The devil is in the detail. Cryogenic preservation in liquid nitrogen is the method of choice. Preserved in straws or cryovials, yeast strains will remain unchanged for decades, and most probably centuries under such conditions. Done correctly this technique creates an environment in which the yeast cells are placed in a state of suspended animation. Most importantly the process has no negative effects on genetic or physiological properties of the cells. Viability of the cells is also maintained under these conditions.

Of course you might be thinking, “can’t I just sub-culture my yeast on agar slopes every few months?” Of course you can, but it’s rather like encoding your brewery operator instructions in the minds of your operators, relying on them – in their own way – to explain how things work to each new member of staff as the need arises. Inevitably, things will drift. Nowadays you’ll write things down, ‘standard work’, ‘work instructions’ – right? That way you’ll reduce the chance of this drift. That’s pretty much how cryopreservation works for brewing yeast. It locks down what you know works.

Unsurprisingly, the advantages of yeast cryopreservation come at a cost. A need for specialist equipment, specialist staff, and access to a reliable source of liquid nitrogen are just three. Staff safety is paramount, and precautions have to be taken to protect anyone using liquid nitrogen from the potential suffocating effects of oxygen starvation and nitrogen gas.

In practice, it’s usually best to have two types of cultures – master cultures and working cultures. Given sufficient storage space you should have enough working cultures to produce all the yeast you need for many months ahead, and ideally many years ahead.

Mistake proofing of cryogenic preservation systems is very important. There’s no point in doing a great job in preserving your yeast if you run the risk of picking out the wrong one and growing it up in your yeast propagators and brewery fermenters.

Back-ups are critical. No single liquid nitrogen facility is bullet proof. A single interruption to your liquid nitrogen supply could spell the end for your customers. Two completely independent systems in different locations are what’s needed. For example, in our own operations we have one cryogenic storage facility in Denmark, and another in the UK – both storing exactly the same yeast cultures. When it comes to disaster recovery procedures, it’s important to know they are in place, and have been proven to work – the equivalent of having a fire drill for your yeast preservation. To an extent ISO 9001 and HACCP systems can provide reassurance in this regard. But there’s no substitute for a healthy dose of paranoia. Be afraid – be very afraid! Expect things to go wrong, then do everything you can to prevent such events from occurring. Then do more. It’s too important not to.

As before, everything that you do in this area has to be verified. There’s no use saying that the preservation has conserved the viability of your yeast unless you have the data to prove it.

Routine yeast culture supply

Slope cultures dispatched to breweries from a single validated audited production site with a back-up production facility available as part of your risk management plan

Nowadays most lager breweries propagate their yeast every week of the year. Or, in the very least, every second week. If you are going to let your yeast run for six to eight generations and are filling six to eight fermenters a day, that’s what it takes. It stands to reason that your aim should be to make every single one of those yeast propagations identical to one another. That has to start with the first stage of the propagation.

Typically that involves inoculating about 10 ml of wort with yeast growth from a slope culture. That yeast can either be taken from the slope using an inoculating loop, or by washing off all of the cells from the slope and using that as the inoculum. Either way, when used once a yeast slope culture should be discarded. Slope cultures should be treated as ‘disposable’. To use them several times is to invite inconsistency in the early stages of propagation which can only become magnified as the culture enters its working life in the brewery.

Yeast slope cultures can be supplied by competent brewery support laboratories like our own. You’re going to need somewhere between 26 and 52 yeast slopes a year, usually delivered every six to eight weeks. On receipt in the brewery cultures should be stored in a locked fridge, or a fridge in a locked room. The refrigerator should be dedicated to yeast culture storage and be of a ‘non-domestic’ type to avoid the risk of temperature cycling (due to auto-defrost functionality).

An alternative to yeast slope supply is the use of ultra-pure dried yeast cultures. The Alfred Jørgensen Laboratory pioneered the development and use of this format of culture many decades ago. Although deployed by a hundreds of breweries all over the world, it remains something of a well-kept secret. This format is the one of choice when cool transport and storage cannot be assured, or when laboratory facilities are not available in the brewery. These dried yeast cultures are supplied in units of 50 g. Each is sufficient for inoculation of a single Carlsberg flask – enough to initiate a propagation in a brewery yeast propagator. By using this format of culture you can by-pass the need for laboratory propagation steps.. While this can save you time, money and equipment, perhaps the biggest benefit of this approach is the flexibility it provides you with in the case of a failed yeast propagation.

On those (hopefully) rare occasions when brewery yeast propagations fail quality tests (for example due to contamination with foreign microorganisms) production delays caused by having to wait for the laboratory to propagate a new yeast culture from slope can be both frustrating and costly. However, by using ultra-pure active dried yeast cultures and thus by-passing the laboratory stages of the propagation, several days can be shaved off the time needed for yeast propagation.

Quality assurance

Cultures tested prior to dispatch to assure identity, purity, performance and freedom from microbiological contamination – performance of all test methods regularly validated

It’s all too easy to assume that if your laboratory people have prepared your yeast cultures in the usual way, everything will be fine. Don’t forget however: when you assume you make an ‘ass of u and me‘. Rather than reply on assumptions, it’s much better to assure the culture quality.

All yeast cultures used in a brewery should be checked to assure their identity, using either microbiological tests and / or genetic tests such as DNA fingerprinting. Checks on culture purity have to be made, to ensure that the culture is pure and homogeneous. Giant colony morphology on WLN agar works well for this purpose, supported by DNA fingerprinting. Checks for microbiological contaminants have to be made too – both bacteria and wild yeasts. And, as always, the methods used for these tests have to be validated to assure their performance.

Secure shipping

Cultures dispatched under temperature-controlled conditions using tamper-evident packaging and appropriate documentation – proactive track and trace of shipments

First and foremost in shipping of brewery yeast cultures is the issue of security. All the work put in to ensure that the right yeast is dispatched in the right condition will come to nought if its integrity during shipping and transport cannot be guaranteed.

Slope cultures should be shipped on ice in insulated containers. Packaging should be tamper-evident to make sure that if anything untoward has happened to the culture it is immediately evident to brewery personnel. Web-based track and trace functionality allows both sender and receiver to know where the cultures have been at all times.

Technical support of the yeast supply chain

Proactive testing of yeast samples from every brewery – access to yeast and fermentation expertise for rapid loop closure – web-based reporting to keep everyone informed

Despite the best raw materials, brewing equipment, people and intentions, things do sometimes go wrong in the brewery. When they do, it’s important to be able to eliminate as many possible root causes of a problem as quickly as possible. This is where centralized yeast supply can come into its own. Since the same yeast culture from the same cryogenically-preserved yeast stock culture has been grown, tested and shipped under exactly the same conditions for every single brewery you run, any problem which afflicts one brewery should also affect the others to a greater or lesser degree. While this is a risk if you allow things to go wrong in the yeast supply chain, if you commit the resources to get it right it can be a great asset. Thus knowing that the same yeast in the same condition from the same stock culture has been used in every brewery can be used as an aid to diagnosis of yeast- and fermentation-related problems.

Early access to yeast expertise can generally lead to more rapid resolution of process and beer quality problems, greater confidence in yeast and fermentation, and more sure-footed loop closure.

Excellent record keeping within the context of a robust quality management system plays an important part in this.

Conclusion

There’s a lot to get right in running multi-site brewing operations, and a lot to potentially go wrong. Centralized yeast supply can be used to increase production efficiency, reduce risk, and increase the speed with which problems are resolved. In terms of finance, yeast supply management costs about 0.02 – 0.1% of the cost of malt supply. Now if malt was responsible for 1,000 – 5,000-times more problems than yeast that difference may be justified. But the fact is that brewers have evolved many ways to cope with poor quality malt. Coping with poor quality yeast is a different challenge altogether.

Interested in finding out how Cara Technology and our Alfred Jørgensen Laboratory can help manage your yeast culture supply? Contact us – we’ll be happy to help.

Secondary to this branding message, brewers attempt to increase a product’s appeal to consumers by affiliating it with one of many specific beer styles. Examples include ‘Amber Ale’, ‘Dry Beer’, ‘Irish Stout’, ‘Pale Ale’, and ‘Pilsener’. It is difficult, and many would argue impossible, to get consensus on the characteristics of each of these beer styles. Some organizations – for example, those established by home brewers with no commercial interests, have attempted to define such beer styles in terms of chemical and physical properties such as original extract, alcohol strength or colour. Others have attempted to define the styles by the ingredients used to make them, or the processes used to convert those raw materials into beer.

Many beer writers find the ‘beer style’ a convenient device for categorizing products. However, it’s easy to see that there are often many points of disagreement among well-respected beer authors on the key aspects of many beer styles. To an extent this is understandable. Beer styles are not static relics of the past. They are evolving, living entities, shaped year on year by consumer trends and innovative brewers.

For example, traditional European pale lager beer is made using only malted barley, hops, yeast and water. As a result it is a flavoursome, full-bodied type of beer. More than 120 years ago brewers in many parts of the world, including North America, Asia, Africa and Latin America discovered that by substituting a portion of the malted barley for so-called ‘adjuncts’ (such as maize, rice or sugar) a lighter, more refreshing beer could be produced. Ideal for hotter, more arid climates. Today, it is this type of ‘new world’ lager that dominates the international beer landscape. Nevertheless, the original all-malt, full-bodied version of the beer continues to be made in Europe and elsewhere – or something close to it at least. The original type of malt used to make pale lager beers was kilned with coke, which released arsenic into the malt and the beer made from it. Thankfully, that’s no longer done.

These old and new styles of Pilsner beer – all malt, or made with adjuncts – sit side by side in the marketplace, linked by a common style name. Variants of each type have evolved and become established to different degrees in different markets. For example, when first introduced ‘new world lagers’ had bitterness levels which were comparable to those of their ‘old world’ counterparts. Today, the levels of bitter substances in ‘new world lagers’ are much lower, a trend which has been driven by consumer preferences and the brewers’ ability to respond to those preferences.

In addition to brand and style, government organizations often require additional product categorization, providing for designations such as ‘light beer’, ‘low alcohol beer’, ‘non-alcoholic beer’, ‘export beer’ etc. These categories tend to differ from one country to another. Beer categorized as ‘non-alcoholic’ in one country may be categorized as ‘low alcohol’ in another. The need for such categories is primarily driven by fiscal requirements – a way of demarcating beer in one tax category from another is needed, with sufficient constraints included to limit the risk of new products falling outside of the tax categories which have been set, such as happened in Japan in the 1980s and in East Africa in the 1990s.

Occasionally, governments or alliances of governments have provided protection for specific beer designations. For example, the hybrid brand and style name ‘Newcastle Brown Ale’ can be used only for beer brewed to certain specifications within a defined distance from the City of Newcastle in England. Allocation of provenance to beers in this way is exceptional and there are very few examples.

The specific case of ‘Pilsener beer’

‘Pilsener beer’ – sometimes referred to as ‘Pilsen’, ‘Pils’ or other variations, originated as a style in the Czech town of Pilsen in 1842. This new type of ‘pale lager beer’ become very popular and soon came to dominate the beer market in that location. Brewers from outside the region adopted the style to different degrees, but the style name proved very popular and has been used by thousands of breweries all over the world for more than a Century and a half.

Today, if one were to compare the characteristics of a Pilsner beer native to Pilsen – for example, Pilsner Urquell – with those of a ‘Pilsner’ from other countries in many cases very little in common would be found.

• Pilseners from the Czech Republic are very bitter – most Pilseners from other countries are not.
• Pilseners from the Czech Republic are not very high in alcoholic strength – Pilseners from other countries can be weaker or stronger.
• Pilseners from the Czech Republic are quite dark in colour – Pilseners from other countries can be lighter or darker, depending on the choice of the brewer.
• Pilseners from the Czech Republic often have distinctive flavour characteristics which arise both from the choice of ingredients and the recipe – such flavours are not well regarded by consumers in all markets so Pilseners made for other markets are often made in a different way and from different ingredients to suit the palate of local consumers. A particular case in point is diacetyl – an essential flavour in a traditional Pilsener, studiously avoided in many New World versions of the style.
• The original extract of Pilseners in the Czech Republic exceeds 11 degrees Plato. However, in many markets outside of the Czech Republic original extract values which are lower than this are found. This arises from the fact that brewers have to sometimes satisfy conflicting constraints concerning the categorization of the product for tax and excise purposes and the stylistic categorization of the product.

The nature of ‘true’ Pilsners produced in the Czech Republic is protected by European statute.

However these constraints do not apply to ‘Pilsner’-style beers produced elsewhere, customized for local markets and tastes. In such cases the boundaries of the style lie in the hands of the professional brewing community and its customers – as it should.

When is a Pilsner not a Pilsener (or Pilsner)? Whenever and whereever you like.

Acetaldehyde can be a friend or foe depending on the beer it ends up in and its concentration. In modern pale lager beers, which make up the biggest volume of beer consumed in the world today, concentrations of acetaldehyde are typically 1 – 4 mg/l. At this concentration it adds a little to the background flavour of the beer, save for e a hint of apple character. It mainly imparts ‘fresh’ and ‘refreshing’ sensations to beer.

However some beers can contain higher concentrations of acetaldehyde, in the range 5 – 15 mg/l. At such concentrations the apple flavour is more pronounced and can take on a more ‘emulsion paint’ character which, in beers of higher alcohol content, can have a ‘solvent-like’ top note.

When fermentation and packaging controls are poor, concentrations of acetaldehyde in packaged beer can exceed 50 mg/l. Generally, that’s not good news for anyone involved!

At low concentration acetaldehyde is associated with green apple, bruised apple, emulsion paint, wine (white wine), and sherry flavour notes.

At high concentrations acetaldehyde can contribute a ‘harshness’ to beer. This can affect drinkability, especially at warmer serving temperatures.

Flavour threshold

Older literature on the subject often cites flavour recognition threshold values for acetaldehyde in the range of 10 -20 mg/l. These values are not applicable today (ie they are wrong!). In modern pale lager beers with low sulphite levels, flavour thresholds for acetaldehyde are in the range 2 – 3 mg/l. Actual threshold values vary with beer sulphite concentration due to adduct formation.

Flavour perception

Beer tasters sometimes confuse acetaldehyde with the ester ethyl hexanoate, and with other aldehydes such as isobutyraldehyde. Regular training and validation of assessors is needed to minimize this risk.

Formation and fate of acetaldehyde

Acetaldehyde is formed and removed at several stages of the beer production process.

• It is formed during wort boiling (via Strecker degradation)
• It is formed by brewer’s yeast from fermentable wort sugars during the early to mid part of the fermentation
• It is reduced by yeast to ethanol during the latter stages of the fermentation and during beer maturations
• It is reformed in packaged beer by oxidation of ethanol after removal of yeast

Formation of acetaldehyde during wort boiling

Low concentrations (a few mg/l) of acetaldehyde are formed during wort boiling through Strecker degradation. Some of the acetaldehyde may bind to wort proteins at this stage, to be released later. Acetaldehyde in this form is resistant to reduction by yeast. Drip back of condensate in the brewing kettle can lead to higher than normal levels of acetaldehyde in wort at the start of fermentation. Regular checks on the kettle stack and condensate system are needed to guard against this.

Formation of acetaldehyde by yeast during the early to mid stage of fermentation

Acetaldehyde is produced by yeast during the fermentation as an intermediate in the formation of ethanol. The amount formed relates to the efficiency of the glycolytic pathway (ieconversion of acetaldeyde to ethanol) and the activities of competing metabolic pathways (eg conversion to acetate and then to acetyl CoA for lipid synthesis).

Reduction of acetaldehyde by yeast during the latter stages of fermentation and during the maturation process

During the latter stages of the fermentation production of ethanol (and hence acetaldehyde) slows. Yeast can continue to reduce acetaldehyde concentrations in green beer after the primary fermentation is complete. Reversible binding of acetaldehyde to sulphite ions can reduce the rate at which both are eliminated at this stage.

Their are several enzymes responsible for reduction in acetaldehyde concentrations:

Alcohol dehydrogenases

• Several different types are found in brewer’s yeast – some have broad specificity, others act on a narrower range of substrates
• They are coded for bythe ADHI, ADHII and ADHIII genes
• ADHI is the gene which is most active in fermenting yeast – its activity falls off during the latter stages of fermentation

Acetaldehyde dehydrogenases

• This mitochondrial enzyme seems to be important for elimination of acetaldehyde at the end of fermentation (being involved in conversion of acetaldehyde to acetic acid)
• It uses either NADH or NADH as a cofactor
• The enzyme itself is formed early in the fermentation in response to exposure of the yeast to wort oxygen

Formation of acetaldehyde through chemical reactions after removal of yeast

• Following removal of yeast from green beer oxidation of the beer leads to acetaldehyde formation
• This is a non-enzymic process – it does not require the presence of yeast
• It does not involve direct reaction of the acetaldehyde with oxygen, but is related to  the redox potential of the beer
• With modern standards of oxygen control in breweries, formation of acetaldehyde in this way should be minimal
• Where oxygen control is poor in-process or during packaging, acetaldehyde can form in beer during storage in pack

Control of acetaldehyde concentrations in beer

Yeast strain

• Brewer’s yeast strains differ considerably in their capability to achieve low levels of acetaldehyde in beer
• Activities of alcohol dehydrogenase (ADH) and acetaldehyde dehydrogenase (ALDH) are very important for reduction of acetaldehyde in the later stages of fermentation and during maturation
• Mitochondrial mutations are generally detrimental to the efficiency of acetaldehyde reduction
• Mutations in flocculation genes can lead to a change in flocculation character of the yeast – greater, more aggressive, flocculence means fewer cells in suspension to eliminate acetaldehyde from the beer
• Yeast variants (mutants) present in a laboratory yeast culture can inadvertently be selected for or against depending on yeast propagation processes, yeast cropping practices and yeast handling practices.

Wort quality

Important wort quality factors for acetaldehyde control include:

• Concentration of wort amino acids (FAN)
• Yeast flocculation-inducing factors (including premature yeast flocculation factor – PYF)
• Available wort zinc concentrations
• Wort dissolved oxygen concentrations
• Timing of wort oxygen additions
• Wort suspended solids concentrations (eg trub)

Fermentation practices

Important fermentation practices for acetaldehyde control include:

• Yeast pitching rate
• Yeast ‘health’ and ‘cell age’ (determined by yeast cropping and handling practices)
• Fermenter depth
• CO2 top pressure during the fermentation
• Fermentation temperatures
• Layering of vessel contents in the fermenter

Conditioning practices

Important conditioning practices for acetaldehyde control include:

• Tight control of suspended yeast cell count
• Control of yeast metabolic activity
• Conditioning temperatures
• Dissolved oxygen concentrations in the green beer
• Layering of vessel contents

Filtration practices

Important filtration practices for acetaldehyde control include:

• Minimization of dissolved oxygen concentrations during the filtration process
• Introduction of materials that have a negative effect on beer redox potential (for example beer-soluble iron from filter aid)

Packaging practices

Important packaging practices for acetaldehyde control include:

• Minimization of dissolved oxygen concentrations in the bright beer
• Minimization of dissolved oxygen concentrations during the filling process
• Temperature control during the pasteurization
• Note also that some types of packaging materials (specifically some types of PET bottles) can leach acetaldehyde into the beer during storage

The importance of brewery hygiene

• Poor brewery hygiene can impact on beer acetaldehyde concentrations both directly and indirectly
• Growth of acetic acid bacteria (Acetobacter spp and Gluconobacter spp) can change the redox potential of the beer leading to acetaldehyde production from ethanol
• Growth of coliform bacteria (such as Obesumbacterium proteus and Rahnella aquatilus) in fermenting wort can lead to nitrite production, reducing the yeast’s ability to eliminate acetaldehyde at the end of fermentation and during maturation
• Lactic acid bacteria (Lactobacillus spp and Pediococcus spp) can bring about premature flocculation of yeast, reducing the numbers of yeast cells available for elimination of acetaldehyde at the end of fermentation or during the maturation process
• Growth of Zymomonas spp in beer leads to formation of high concentrations of acetaldehyde – these organisms require monosaccharides such as glucose for growth so they are not common contaminants of lager beers; ales remain at risk though

The effect of acetaldehyde on yeast cells

• Acetaldehyde is toxic to brewer’s yeast
• It binds to cellular proteins and can inactivate enzymes within the cells
• It can also be mutagenic to yeasts
• Interestingly, when yeast cells are exposed to acetaldehyde many genes related to formation of volatile sulphur compounds are also expressed

Conclusion

Congratulations if you got through all the way to the end of the article. If you have, at least you know where to find the information you need should you ever have an acetaldehyde problem in your brewey.

One final point – for some beer styles acetaldehyde is a desirable flavour characteristic – French country-style beers being one example.

This paper – entitled “Über die von der molekularkinetischen Theorie der Wärme geforderte Bewegung von in ruhenden Flüssigkeiten suspendierten Teilchen” (“On the Motion of Small Particles Suspended in a Stationary Liquid, as Required by the Molecular Kinetic Theory of Heat”) - concerned a problem that had puzzled Einstein for some time. Why was it that tea leaves, when stirred in a cup of tea, moved to the centre of the liquid over time, rather than move to the outside. In this paper he derived a mathematical solution to the problem, explaining the forces at work in this phenomenon.

Fifty five years later in 1960 and the fruits of Einstein’s labours were first applied by brewers in Canada as the basis for the efficient clarification of hot wort and its separation from trub. H Ranulph Hudston working in Molson’s Montreal Brewery in Canada was the first to make use of this phenomenon to separate clear hopped wort from trub at the commercial scale. In doing so he allowed the brewery to eliminate the use of their hop backs, which had been the dominant technology for close to 200 years.

In a paper published in the MBAA Technical Quarterly in 1969 Hudtson recounted that

“prior to the introduction of the whirlpool concept, hot wort receivers in the brewery were vertical, cylindrical, flat-bottomed vessels, with a diameter roughly equal to the working depth of 16 feet. They were equipped with an umbrella-shaped device suspended near the top of the vessel. The wort was pumped from the top of this device to cause a cascade for hot aeration. After a settling period of 30 to 40 minutes the wort was run to the coolers, being drawn from just below the surface by means of a float pipe.”

Hudston’s change to the vessel was quite simple, he move the wort line from the top of the tank to the side of the tank to allow the wort to enter the vessel tangentially.

When the first brew was put through the tank, it was noticed that after emptying, the nature of the dregs of wort and trub was slightly altered. Instead of being fluffy and particulate, some compacting and agglomeration had taken place.

After a little more experimentation relating to the positioning of the tangential inlet and the flow rate of the wort, Hudtson soon had a voluminous, compact trub pile in the centre of his whirpool after a short stand. His finding changed the brewing landscape – today, almost all large scale commercial breweries use whirlpools for hot wort separation. Numerous patents have been filed by equipment manufacturers relating to subtle design modifications of he whirlpool, but the basic forces at work remain those so elegantly described by Einstein more than 100 years ago.

Getting a whirpool to work just right is still something of a black art, involving a combination of raw materials quality, brewhouse procedures, and equipment performance.

We have Einstein to thank for many things: trub-free fermentations and lower extract losses are just two of them.

Off-flavours

Off-flavours are odours, tastes and mouthfeel characteristics which have been formed in the product or process through chemical or biochemical reactions, sometimes with the involvement of enzymes and / or microorganisms. To an extent, process and product design pre-dispose a product to development of off-flavours and constant vigilance is needed on the part of the brewer to resist this flavour inertia.

Examples of off-flavours include:

• Acetaldehyde
• Acetic
• Astringent
• Burnt-rubber
• Butyric
• Diacetyl
• DMS
• Ethyl acetate
• H2S
• Indole
• Isovaleric
• Lactic
• Leathery
• Lightstruck
• Mercaptan
• Mousy
• Onion
• Oxidized
• Papery
• Tobacco
• 4-Vinyl guaiacol
• Yeast bite

Taints

Unlike off-flavours, taints are foreign to both the product and process. They come from ‘outside’, getting into the product via vectors such as liquids, solids and gases.

Examples of taints include:

• Alkaline
• Bell pepper
• Bromoanisole
• Bromophenol
• Chloroanisole
• Chlorocresol
• Chlorophenol
• Cresol
• Earthy
• Iodoform
• Metallic
• Mouldy

In addition to the basics of using good quality raw materials, well maintained and well designed brewing equipment, well thought out recipes and processes, and – of course – skilled, experienced brewers to make your beer, a highly trained taste panel is a great help in the fight against off-flavours and taints. Once tasters have been taught to reliably recognize each of the flavour attributes listed above, eliminating the defect is made so much easier.