After our mash process has completed (about 4 hours), we cool it down to a temperature of ~ 25 celsius (77 Fahrenheit) in preparation for fermentation. Fermentation is the chemical breakdown of a substance by bacteria, yeasts, or other microorganisms, typically involving effervescence and the giving off of heat. In our case, we use yeast, a micro-organism that feeds on sugar in our mash and turns it into ethyl alcohol and CO2. There are many ways to add yeast to the mash (often debated among distillers) – we just sprinkle it on top and let it do its thing.
Fermentation is arguably the most crucial step in distillation because it is where the chemical process of esterification occurs and flavor molecules or ‘esters’ are created. Most of the taste (and all of the alcohol) is made during fermentation, not during distillation. There are many other factors too lengthy to discuss here that impact fermentation (yeast strains, temperature, pH, water quality/temperature), but rest assured, a bad fermentation will result in a bad spirit – especially when making taste rich spirits such as a single-malt whiskey.
When fermentation is complete, we end up with liquid referred to as ‘wash’, sometimes called a ‘bad beer’, at ~ 7-8% alcohol. The wash is what we charge our still with and begin the next step in our process…