Category Archives: Fermentation

Maximizing Whisky Yield: Part 1 – Key Differences and Optimization in Wash Production

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This is the first in a series of three posts detailing how I worked with a new English whisky distillery to define and optimise their wash production.

Background

In November 2023 I was called by a new craft whisky distillery to help them with two distinct processing problems: stuck mashes and incomplete fermentations. However this soon grew into a project to optimise the yield of their wort production.

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Structure

This first post explores the key differences between wort production for beer and wash production for whisky. Both are sugar solutions derived from malted barley but understanding the key differences between the two methods is vital to the quality of the end product.

The second post covers how I defined the process control parameters from scratch using ‘on the hoof’ experimentation on the live process (a skill I developed working in a production based tech support roles in the chemical industry).

The final post (link to follow) looks at changes we implemented in the brewing equipment. What I arrived on the project the brew kit had already been installed, but some minor low cost changes have significantly reduced the process time, which in turn have positively impacted both quality and yield.

Part 1 – What are the key differences between wort (beer) and wash (whisky) production?

Why are the processes different?

The primary driver of whisky wash production is yield. Because the optimal ABV of the fermented wash is around 8.5% ABV, the quantity of available sugar left in the weak worts after the end of the sparge would be considerable if a beer wort method were used – in this case the weak worts at the end of run off would be 1.050-1.055 (approx 140 g/L sugar content). Additionally, it is desirable in beer to have unfermented complex sugars in the final beer to give body and a residual ‘sweetness’. Beer worts typically show an attenuation* of 75-80%. If your aim is to maximise the yield of alcohol per tonne of malt both of these factors would be considered a loss to yield. With whisky production, the optimal yield is 415 litres of pure alcohol per tonne of malt input.

It is always important to remember that the (desired) flavour of whisky is defined by the process by which it has been made. And since the nature of the process was fixed before the underlying consequences on the biochemistry of the process were fully understood it is important to (1) follow traditional methods to give the traditional/desired flavour; (2) understand and manage the shortcomings or “features” of these methods to achieve a consistency of yield to, and quality of final product.

*percentage conversion of sugars to alcohol

Malt colour-gradientMash temperature

Traditional wash production uses a mash tun, and normally you would think that this would limit you to an isothermal mash. But with whisky wash production a pseudo step mash is carried out by initially mashing at a low temperature (ideally just above the gelatinisation temperature for the quality of malt, which varies by the season). This favours the production of immediately fermentable sugars. It is then sparged at 75 C to both wash out the sugars already formed and also to raise the mash temperature to activate alpha-amylase thus form and extract complex sugars also.

Run off method

To maximise sugar extraction during sparging, most of the strong worts are run off before the sparge is started. Often the liquor:grist ratio is higher in wash production which means there is more volume to run off. This step needs to be carefully designed to avoid running off too much liquor which could lead to a stuck mash.

No wort boil

Wash is run off directly into the fermenter, it is not boiled. There are a number of consequences to this:

  • Lactic acid bacteria (LAB), present on the surface of all barley malt remain viable and active in the fermenter – they are not denatured by a boiling stage. This needs to be accounted for (see below)

  • In a well run process, active enzymes – amylases but also importantly limit-dextrinase – transfer with the wash into the fermenter

  • Because the wash has not been boiled (which causes vigorous mixing) or recirculated in the copper the wash in the fermenter cannot be directly sampled to gain a representative sample for SG / OG control.

These consequences all need to be managed if you are to achieve product consistency and high yield.

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Managing lactic acid bacteria (LAB).

As soon as the wash is formed, LAB start acting on the maltose to form ethyl lactate. Because they convert sugars which could form alcohol this can have an economically significant effect on the yield. For this reason, yeast is pitched into the strong worts, early in the transfer into the FV. The aim is for the yeast to out compete the LAB and minimise losses of sugar to ethyl lactate at the start of the fermentation.

The fruity flavour imparted by ethyl lactate is an important characteristic of whisky so careful management of the fermentation is required to ensure that the level is consistent from batch to batch. At the end of the yeast fermentation, LAB are able to metabolise other oxygenates, such as malic acid to form ethyl lactate. To ensure flavour consistency the length of time that the fermentation is left to stand post completion of yeast action needs to be controlled. It is normal in small scale whisky production for multiple batches of wash to be required to fill one cask with spirit. Because of the impact of five day working not usually possible to allow every fermentation to run for the same length of time, and from this come the terms ‘shorts’ and ‘longs’ describing wash fermentations which have been been completed and distilled within the week or run for longer over a weekend. Each cask of spirit should contain the same proportion of shorts and longs and thus production should run to a regular pattern each week.

Malt enzymes in the fermentation

It is essential for the enzyme limit-dextrinase (from the malt) to remain present and active in the fermentation. For this to happen, the time that the wash remains hot post saccharification needs to be minimised i.e. you need to run off and cool the wort as quickly as possible once starch conversion is complete. It is this enzyme which breaks down the unfermentable sugars in the wash into fermentable sugars which allows a far higher attenuation by the yeast. A typical whisky wash has an OG of 1063, without limit-dextrinase the fermentation would end at an SG of around 1013, with it present the fermentation continues to an SG of 996-1000.

Wash SG control

Ideally the FV (often called a wash back) needs to be able to be recirculated so that the wash gravity (SG) can be accurately measured and controlled, at very least during process commissioning. Remember that wort gets progressively weaker during its transfer, and thus the FV is stratified ‘by design’ and thus non-homogenous. Recirculation could not easily be retro-fitted to the kit I was working on, so I developed and proved an alternative method which I will discuss in my next post.

3rd water

Once all the wash has been collected, the mash bed is sparged again, at a higher temperature still, and this liquor is used for mashing the next batch of malt. This liquor is called 3rd water.

  • First water – liquor used to mash the grist.

  • Second water – sparge liquor sent forwards to the FV.

  • Third water – second sparge liquor containing residual sugars, recycled into the following batch.

In a large distillery, the 3rd water is likely to be used within the hour. In a craft distillery it is likely you will only be making one or two batches of wash per day so you need want to hold some of your 3rd water overnight. What is key here is to keep it above 70 C so it remains free of the effects of bacterial or wild yeast contamination. However, for anyone familiar with smaller scale brewing you know you want your mash water at or close to strike temperature (usually 70-74 C) at the start of the day anyway so it is normal to heat it to 10 C above this the night before knowing it will come in about right the next morning in a well insulated hot liquor tank.

Improving your margin…by maximising your batch size.

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We are living in a challenging time for the small scale brewer. Raw material and energy costs are at an all time high, yet our customers has less disposable income. To maintain your margin without sacrificing quality one, excellent method is to max out the capacity of your brewery. This article is aimed at small brewers, not those with vessels to hold their last runnings to use as the start of the next sparge and the like.

Which vessel is going to limit you?

This is the first question you need to ask – which of your vessels is going to limit your output? Assuming you brewery equipment was bought at the same time, it is unlikely that your mash tun will be your limiting factor. This is likely to have been designed to brew ABV’s higher than your core range beers. So you need to know the volume and thus working capacity of your copper and your fermenters.

It is easy to estimate the volume of these vessels. Most coppers are cylindrical and thus the total volume is easily calculated.

Volume of a Cylinder = Π . r2 . h

The volume of flat bottomed fermenters can be calculated the same way, but if you are lucky enough to have cylindroconical fermenters you need also to calculate the volume of the cone at the base and add this to the volume of the cylindrical section.

Volume of a conical section = Π . r2 . ⅓H

But of course there is a difference between the total volume and the ‘working’ or useable volume. For a copper this is 80% of the total volume. For a fermenter it will be in the range 80-90% depending on variety of factors.

How to maximise the capacity of your copper

Wort-Boiling

There are two options here. If you don’t want to alter your recipe then to maximise the volume that your copper can safely boil you can reduce the foaming that occurs at the start of the boil. As the proteins from the malt denature and drop out of solution they act as nucleation points for the bubbles of the boil and other proteins aid foam stability. This can lead to a deep head of foam during the first 10 minutes of the boil. There are commercial antifoaming agents which can be added at this stage of the boil, but you may not know that the natural product versions of these are actually a hop extract. So if you add around 5% of your hop bill just before the start of the boil (i.e. First Wort Hops) these will reduce foaming without you adding cost or anything artificial into you beer.

Another option would be to consider taking a small step towards high gravity brewing. You can aim for a pre-boil gravity 10-20% higher than your designed post boil gravity, knowing that you can liquor back at the end of the boil either directly post boil, or during the transfer.

How to maximise the capacity of your fermenter

Filling fermenter - foam

Here again, foam management is key to maximising your capacity. Medium and larger scale breweries would normally fill their fermenters from the bottom to minimise foam formation. As well as increasing capacity it also aids head stability in the final beer. Think of the foam capacity of beer being a fixed value over the whole life of the beer, from manufacture to the customers glass – the more foam you form in the process, the less potential for foam (head) there is in the final beer. In bottom fill operations the wort is oxygenated in-line on the way to the fermenter. However in micro breweries oxygenation is often achieved by top filling the fermenter, allowing the splashing of the work to entrain oxygen and thus avoid the need to buy bottled oxygen.

If you top fill your fermenters to oxygenate the wort the volume of foam can be considerable and limit the capacity of the fermenter. Here an antifoam agent such as Murphys FD20PK or AB Vickers Foamsol can be added during the first 10% of the transfer to dramatically reduce the foam and thus increase your fermenter capacity. I was recently able to increase the fermented volume at a brew-pub client by 7% using this approach.

None of the concepts I have highlighted above require the purchase of any additional equipment. It is not uncommon for a brewery to increase it’s capacity by buying double sized fermenters and filling with two batches of wort each day, but this is likely to mean employing extra staff or paying overtime – so whilst it will increase your capacity, the impact on your margin will be minimal in comparison to the simple optimisation methods I’ve detailed above.

The best approach

When you have decided which process stage you want to focus upon, the best approach is to make a number of step wise changes towards what you have estimated as your maximal capacity. But remember that each increase will need to be in increments of cask volume (i.e. 42 litres for an extra Firkin or 21 litres for a Pin). Gaining an extra 3/4 of a cask does you no good at all!

If you would like help maximising the batch size of your microbrewery, then please give me a call.  Similarly, if you would like someone to brew on your kit to cover times of peak output or to cover holidays (without having to employ an additional person full time) then this is another service I am pleased to offer.

How to perform a diacetyl test – and why you should.

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What is diacetyl?

For yeast cells to grow they need nutrients, some for energy and some to build new cell material to enable multiplication. That which they cannot draw from the wort, the yeast needs to synthesise from simpler starting materials. During the synthesis of the amino acid valine, a by-product is diacetyl.

Diacetyl chem structure pic

The challenge with diacetyl is that it has a low taste threshold and it tastes of butterscotch, not a flavour we want in most beers.

How is diacetyl formed?

It is good to understand this, as it underpins how the diacetyl test works. As with most biochemical pathways, the formation of diacetyl is a multi-stage process. It is important to understand that up until the penultimate stage these steps are enzyme catalysed (i.e. fast) but the final step from α-acetolactate (AAL) to diacetyl is a simple but slow chemical reaction. With AAL being capable of being formed faster than it is consumed, a residual concentration can build up in the final stages of fermentation. This is especially true in lower temperature fermentations. Thus once your ale / lager has reached its terminal gravity it may not taste of diacetyl, but if AAL is present, it will be formed with time in the final package. Thankfully yeast also contains an enzyme which will reduce diacetyl to 2,3-butandiol which has a far higher taste threshold and this eliminates the off flavour issue. Thus the diacetyl rest, a period of warm conditioning at the end of fermentation, which allows the AAL to convert to diacetyl and under conditions where it can be consumed to form something essentially flavourless. Cool down the green beer and this enzyme cannot act.

So what is a diacetyl test and how to I perform it?

You could take a sample of your green beer and inject it into an HPLC and see if AAL is still present, but if you don’t have a spare £25k burning a hole in your pocket there is a far simpler and cheaper method:

Take two samples of your green beer, 50 ml each is enough, into sealed bottles. Place one into the fridge (the control) and drop the other into a jug of hot water at 60-70 C, chances are you have some hot liquor to hand which would be ideal for this. Leave the sample in the hot water for 20 min then remove and cool. Then all you need to do is to taste both samples.

  • Can you taste butterscotch in the heated sample (having the control sample to compare against makes this assessment much easier) – If you can then you have some AAL still present in your green beer which will form diacetyl with time. The green beer needs longer to warm condition so hold at 16-20 C for another 24-48 hours and then run the test again.
  • There is no diacetyl taste to either sample – your beer is ready to chill and move forwards.

My experience

Residual AAL / diacetyl is present at the end of the primary fermentation of some recipes but not all. The key factors are the choice of yeast, malt bill and fermentation temperature. Some combinations will require a diacetyl rest, some will not. Some craft breweries are paranoid about diacetyl in their beer and warm condition all their batches, but unless you are making a lager, this is an unnecessary loss of brewery efficiency. When you are running a new recipe then run the test for the first three gyles. If the test comes out negative at the end of each primary fermentation then unless you change anything it always will. Carry out warm maturation only on the beers which need it. Beer design is, in part, an art but its manufacture is certainly a science.

If you find yourself with a beer design where AAL / diacetyl is present at the end of the primary fermentation you do have another option. That is to add an exogenous enzyme (AAL decarboxylase / ALDC ) into your FV at the start of fermentation to guarantee that all the AAL will be quickly reduced to acetoin and no diacetyl will ever be formed.

Would you like help with the consistency of your beer quality? If so give me a call and we could arrange a phone / video consultation or if you are local I could come out and help you in person.