Whiskey Fermentation Is More Than Sugar In, Alcohol Out

Who do we thank for whiskey? Is it the distillers and the distillery owners? The bartenders? The grain-growers? The malters? Yes, yes, yes, and yes – but there’s somebody – or something – missing from that list.

Yeast. Without yeast, there would be no fermentation, and without fermentation, there’s no whiskey. Heck, without fermentation there’s no alcohol (perish the thought!).

Fermentation is a step that’s often glossed over when talking about whiskey production. It’s not the sexiest part of making spirits. Fermentations look like a big, bubbling vat of either porridge or flat beer, emitting strange smells along the way.

So what is fermentation? When we’re talking about whiskey fermentation, it’s when one or more varieties of yeast are digesting sugars and emitting alcohol as a waste product. In a bigger sense, fermentation is metabolism in the absence of oxygen – bacteria, yeast, and other single-celled organisms transforming sugars and starches into other things by eating them.

That’s the simple story. The chemistry inside fermentations can be elaborate. Some mashes include bacteria like lactobacillus, which give the fermented mash a sour flavor. This is not to be confused with sour mashing, the practice of re-introducing backset or stillage into new fermentations to standardize pH levels from batch to batch.

At various points in the whiskey fermentation process, yeasts create a huge range of different flavor compounds like acids, esters, aldehydes, and long-chain alcohols as byproducts. Some taste great, some taste terrible, and most have a big impact on the ultimate flavor of the distillate.

Human beings have been eating fermented things for a very long time. Before whiskey, there was beer, and before beer, there was fermented fruit. Even animals like monkeys and birds are regularly observed eating – and enjoying! – fruits that have fermented on the tree or on the ground, partaking in the animal kingdom equivalent of an after-work happy hour.