Small scale single malt whisky vs Scottish scale
For many years now I have been researching single malt whisky and trying to maximise my yields. The first ‘problem’ I found was that my fermentation was getting stuck at around 1.020 which is pretty much where it lands for a beer. In order to troubleshoot the problem, I needed to find out out how much sugar was left in the system so I modelled a fermentation mathematically. It was accurate maths, but not 100% replicating the actual process, though producing an appropriate result. Barley has about 80% extraction, so that is the starting point. Of the extractable carbohydrates, 49% goes to carbon dioxide and 51% goes to ethanol. The yeast will use 7-8% of the sugars for their own energy needs. Using these numbers you can estimate how much sugar is left for any final gravity (FG). I discovered that I had 50% of my sugars unfermented.
The trouble is that I was using a method I found on chat forums and it was based on the beer method. I was heating my wort up and denaturing the enzymes (beta amylase mostly) so they stopped chopping the sugars into smaller pieces (yeast can only digest small sugars with 1, 2 or 3 carbons in a chain: glucose, maltose and fructose, and maltotriose). I discovered that I had a time limit after mash-in of 60 mins @ 65C, after which beta amylase would be as good as. I tried this and started getting better results, my mash got stuck at SG 1.010, sometimes it went down to 1.005.
This was much better, but I also discovered that my sugar yield, as calculated from the original gravity (OG) was not high enough. In my research on this I discovered that there was a pH issue and that the mash-in water needed to be between 5.2 (optimum for beta amylase) and 5.6 (optimum for alpha amylase), say 5.4 to hit the middle ground. Once I started doing this I got better results but inconsistent. One of the problems I identified was channeling in the lauter tun and I needed to mix better at mash-in. I was leaving a lot of sugar on the draff because my sparge water was channeling through a ‘hole’ in the draff. The other issue I discovered was that it is not the pH of the mash-in water that needs to be 5.4, it is the pH of the mash that needs to be at this level. The chemistry of the water will determine how much acid needs to be added and if you have soft water the pH of the mash-in water might well need to be 6 and with hard water it might well need to be 5. The important thing to understand is that the malt has its own chemistry that will drive the pH down, but it also has buffers that will limit how far down it will go. The other important thing to understand is that the pH in the lauter tun will be about 0.2 less because it is hot and this releases more H+ ions and creates other reactions that reduce the pH, so you have to cool the sample to 20C to get a reliable result. Every step I took had a series of complications that I had to understand before I could move on. Sometimes it took me 10 mashes to figure out where I needed to look next for answers.
In Scotland you will read that the water used is soft and there is no modification to the water when they mash-in. So I tried this, I used my RO plant to make soft water and I mashed-in and lo and behold, I did not get a good mash, the saccharification was not happening well, the mash was thick and did not drain well and I had to add lactic acid to the mash and mix it all up at the 45 mins mark. Here’s a thing: in Scotland they use 2-3 sparges after mash-in. Let’s call the mash water the first water, and that water will end up between 63 and 64C. The second water (1st sparge) is around 75-78C and will be about 1.5-2 times the mass of the malt used. Then there is a 3rd water (2nd sparege) which does not go into the fermenter; it goes to a hot liquor tank and will be used as first water for the next mash. So, you have this soft Scottish water running through the draff and picking up a little of the wort to make a very weak wort with a completely different chemistry to the original water. I cannot find any data on the chemistry of this weak wort, but I can assume that it is different and when added to the grist at mash-in, creates a lower pH that is perfect for the enzymes. This is how they use soft water with no modification to get an efficient mash. When you are making whisky at a small scale, it is difficult to do the 3rd water so there is only one option and that is to modify the first water. The beer brewers do this and if you will find a spreadsheet to download HERE that will help you calculate what you need to add.
As a result of all this I am now getting much more consistent results from my mash. There is more detail to it all which will come at another time in more specific blogs.
Ok, so I have an efficient mash but my FG was still getting stuck at 1.010. I did consult with a well known whisky producer who said that this is ok in Australia because our barley is grown for brewers, not whisky makers; its diastatic power (DP) is not high enough. I looked into this and lo and behold, this is the case. DP is a measure of the enzymes in the malt and the higher the DP, the higher the quantity of enzymes. The best malt I found had a DP of 370, while in Scotland they get malt up to 680. I also discovered that dry yeast does not have the same attentuation as wet yeast (about 15% less, and when I put this information together, I figured that we were buggered in Australia and would have to accept lower yielding fermentations). Well, we are not completely buggered, we can add enzymes to the fermentation and easily get down to FG 1.000 and for anyone out there wanting to get a better yield, try adding glucoamylase, about 10ml per 100L wort, and watch what happens. It is not that simple, some glucoamylases are derived from fungus and do a better job because they can break 1-6 starch link and a 1-4 link (just trust me, this is important). If you can find an enzyme that has glucoamylase and limit dextrinase, you will be covered for both these linkages.
Another difference I found between small and large scale is the temperature profile. In Scotland they cool the wort to 20C and let it ferment at its own pace. As the yeast starts to work it produces heat, same our bodies, and the wash heats up too. The rate of heating is slow to start but after 24 hours the curve is steep and the wash heads toward 29C and at this point it slows down since most of the sugars are converted to alcohol and the curve levels off after 48 hours at about 33C. My fermenter is a skinny 600m diameter unit and loses heat faster than it can produce it from the 24hr mark onwards. If I started a ferment at 20C it would peak at 24C and cool to ambient quickley thereafter. So I started my ferments at 30C which was involuntary to a degree because my plate heat exchanger (PHE) wasn’t using all its plates and it was difficult to run enough cooling water through it to get the temperature lower. Here’s what happens when the temperature starts too high: the yeast get going real quick and the SG drops real quick and the yeast produces more acids than it normally would and the pH drops to 3.5 after only 18 hours at which time the SG is around 1.018. Within another 12 hours the SG is 1.010 and that is it, end of fermentation! Why? Because from about pH 4.5 all the enzymes are pretty much inactive and all the dextrins floating about are not being chopped up into maltose and glucose, or even maltotriose. The enzymes need about 36-48 hours above pH 4-4.5 to continue their work and I had taken that oportunity away from them with the low pH.
When I dosed the fermenter with potassium carbonate with the yeast pitch, the pH stayed high enough for long enough for the enzymes to work their magic and the SG reduced in a lovely curve all the way to 1.000 with no exogenous enzymes.
So, if you are trying to emulate the Scottish way of distilling but on a small scale, I can tell you that it is nigh impossible. If you want higher yields there are ways to do this as follows:
- modify your first water for mash-in
- if you start the ferment at a higher temperature, dose it with something like potassium carbonate to keep the pH up
- if you start your ferment at 20C, get a system to warm the tank up during fermentation so the yeast remain active (more a winter thing and an aquarium heater will do the trick)
- keep enzymes on hand as a backup to ensure that you always hit a FG of 1.000.
