I have to say that understanding this concept took me quite some time because I could not find any information on it anywhere. There may have been literature that alluded to it, but nothing spelt it out. I was mashing barley and following temperature regimes suggested by others who I assumed were in the know and I was getting great sugar extraction. In fact, I was getting close to laboratory sugar yields, so why was my fermentation stopping short, and why was my alcohol yield so low?
The answer lay in the fermentable sugar yield and it took me about 100 hours of searching and reading and connecting dots. Barley has two enzymes, alpha amylase and beta amylase. Both of these enzymes break starch down into sugar. I should note here that sugar is not only the white grains you put in your tea; it is also a much longer chain molecule made of of many monosaccharides (single sugar molecules). Yeast can only convert the shorter chain sugar molecules into alcohol, so we need to understand how the sugar is produced in order to understand how to generate as much shorter chain sugars as possible.
Alpha amylase is a brute force enzyme that chops a starch molecule at any link it finds and then it moves on. In the process it yields fructose, maltose and long chains sugars randomly. It operates quickest at around 75°C but only lasts around two hours, after which it becomes denatured and will not perform.
Beta amylase is an artisan and carefully chops a starch into a sugar two molecules long, maltose to be precise. It starts at one end and keeps chopping until there is no more starch and a bunch a maltoses. Beta amylase operates quickest at around 64°C but it denatures very quickly; in less than an hour at 64°C it becomes useless.
Here is the trick and the explanation: get your first charge of hot water into your grain and out again within 30 minutes and cool it down immediately to room temperature. This will ensure that a large portion of your beta amylase is preserved and it will continue to break down long chain sugars during fermentation, ensuring you maximise your fermentable sugars and therefore your alcohol yield.
The picture attached shows a simple cooling coil I made that fits inside to 20L bucket I used to drain the wort into. I run tap water through it and after about 5 minutes the wort is about 22°C.
If you read anything else, or watch uTube videos, that do it differently, trust me, they are all wrong. There is a fantastic looking, professional video out there somewhere that has a mashing process very much like beer mashing and I know from experience that at least 50% of the sugars are unfermentable. The reason is that beer requires unfermentable sugars to give it ‘body’ and so beer makers boil the life out of their wort to ensure they kill the enzymes (and bacteria) and maintain the level of unfermentable sugar they are targetting. Do not do this if you are going to distill after fermentation.
Follow the suggestions in this post and you will get about 80% more alcohol – just throw it in your still and watch the spirit flow. For every 1kg of grain you should get almost 1 x 750ml bottle of alcohol at 40% ABV. That’s your target.
Have fun 🙂