THE YEAST MONOLOGUES W R I T T E N B Y L U I S AYA L A
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east1 are at the core of the alcohol industry — without their ability to transform sugars into alcohol we would not have the fermented or distilled beverages we enjoy so much. Yet yeast are often abandoned and left unattended to do their job as if their magical transformation powers were under contractual obligation. Our failure to monitor and support yeast often results in reduced profit margins, even losses and/or altered quality levels for the resulting alcohol. Most of my long-term consulting clients have heard me say that I find it easier to understand yeast than people. This understanding of yeast is construed by some people as having the ability to tell yeast what to do or how to do it, but in reality, it is entirely based on attentively listening to its monologues and reacting to the information yeast is able to share with us.
THE EVOLUTION OF YEAST As surprising as it may sound, scientists still do not agree on why yeast evolved the ability to ferment sugar into alcohol. Sugar is, after all, a great source of energy for all life forms and most of them
use this energy to grow and reproduce, so why would an organism forego the opportunity for biomass generation? The most accepted answer is that alcohol production through fermentation evolved in certain strains of yeast as a defense mechanism. By evolving a tolerance against alcohol (which is needed to produce it), these strains were able to create sanitary environments where other microorganisms would die, paving the way for yeast colony growth and survival once the resources were protected from other yeast, fungi or bacteria. Let’s take a closer look at one of the most popular yeast strains and perhaps the most studied eukaryotic organism besides human beings. When people first read or hear about someone using Saccharomyces cerevisiae to ferment, their initial reaction may be: isn’t that bakers’ yeast? Bakers’ yeast is, after all, better at producing CO2 (to help the dough rise) than at producing alcohol. The answer is that there are over a thousand different isolates of S. cerevisiae, each one with their own specific traits2. Some yeast are better at producing just ethanol (aka “vodka” yeast) while others are prized for their production of
different types of congeners, in different concentrations. Which yeast you should use for your fermentation will depend on many things, including environmental conditions, raw material properties and desired ABV and congener yields. I recommend reaching out to yeast suppliers and relying on their expertise to select the best candidate(s) and then conducting small-scale fermentation trials to validate those decisions. If you selected more than one yeast (because you like the combined congeners produced by them), resist the temptation to pitch them all in the same fermenter, at the same time. Instead, ferment separate batches, each with its own yeast and then distill and combine the alcohols. Having more than one yeast variety in the same fermenter will trigger their “territorial” response and the production of additional biological responses to the perceived threats. Remember that yeast are very protective of their environmental resources and will not be happy to share them with other organisms. Let’s now focus our attention on the messages we may be able to decipher by listening attentively to yeast.
1 The noun yeast is used throughout this article as both singular and plural. 2 Genome evolution across 1,011 Saccharomyces cerevisiae isolates (2018 Macmillan Publishers Limited)
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