When you aim to create a great tasting spirit - fermentation is where it all starts! If your fermentation isn’t good, then there is no way your distilled spirit will be good. For this reason, the variation in the methods used for fermentation, and the results that follow, are as different as the number of craft distillers in the world.
The dictionary definition for fermentation is as follows; “The chemical breakdown of a substance by bacteria, yeasts, or other microorganisms, typically involving effervescence and the giving off of heat.”
In the case of alcohol production, the substance being broken down, could be anything from grapes and other fruit, to rarer cases of milk or proteins. Generally, however, there are certain substances used more than others, you can group most alcohol product fermentations into three categories; Fruits, Grains/Starches and Sugar products.
Depending on what is used as a base for fermentation, there may be further preparation needed before the next step. For example, getting rid of the skins on fruit which can cause bad flavour formation, or using enzymes to break starches down into fermentable sugars. Additional nutrients, needed by the yeast organisms, are also added at this point.
When fermenting for alcohol, you will find that in most cases yeasts are used, these can fall into two categories; yeasts bought from specialist suppliers and wild yeasts. The yeasts bought from suppliers are the most widely used kind, and being living organisms, they are grown in the correct conditions and then packaged and sold.
These bought yeasts also come in two forms, dehydrated and already hydrated. The hydrated form is kept in more or less the same state it is grown in. The dehydrated form is dried out making it easier to store and transport, however it does need to be rehydrated before it can start working again.
The other form of yeasts used are wild yeasts, these can be found all around us on a daily basis, even in the air. Many fruits have their own wild yeasts, for this reason fruits left out for too long begin to break down and ferment on their own. Distillers that go the wild yeast route will in essence let nature take its course, leaving their fermentations open to any wild yeasts in the air or allowing any yeast found in the fermentation base to do its thing.
There are many different types of yeasts in the world but the ones used in alcohol fermentation are amazing little organisms and because they are so amazing, they can also be very needy, in terms of the environment they will work in. Each yeast type has certain conditions in which it thrives. Some of the most important factors for keeping a yeast cell happy are correct sugar levels, oxygen, nutrients, as well as the right temperature and pH ranges.
When the yeast is happy in its fermentation environment, it gets to work, it first begins by using up all of the oxygen along with some of the sugar and nutrients to reproduce. When the oxygen runs out the yeast begins a different process, instead of reproduction, it now begins breaking the sugars down into carbon dioxide and alcohol!
Eventually, the fermentation gets to a point where either there is no more sugar for the yeast to break down or the amount of alcohol present is too much for the yeast to survive in, at this point the fermentation stops.
The Good Stuff
As the fermentation progresses, various types of acids are also formed, depending on the base used, the time taken and how happy the yeast is during the whole process. These acids then bond with alcohol molecules to form something called esters. Esters are in essence flavour and the more esters in a fermentation, the more flavour there will be in the final distilled product.
Unfortunately, more esters aren't always a good thing, as depending on what acid they are formed from, they can create bad flavour. This happens when something has gone wrong in the fermentation, for example the temperature or pH was below the amount in which the yeast was happy. When the yeast is stressed out, the acids formed from fermentation are the bad kind, and when these acids bond with the alcohol to form esters, they too in turn are the bad kind.
In the end, the better a distiller understands his or her yeast and the conditions that it needs to be happy, the better the fermentation will turn out. Thus, a good fermentation is key to a good distilled product