Blinded by Science: Increasing Ethanol Tolerance in Yeast

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November 20, 2015 by fhsteinbart

Yeast Tolerance

Here we see the data on increasing effects of ethanol on yeast populations with concurrent increases in mutative strains.

There was a great article published by the Leuven Institute for Beer Research in Belgium. Their basic research showed that there were heterogenic populations of yeast after several generations from increasing sugar content. This parallels my own observation of increasing the sugar content in my own worts to produce  stronger beers. For example, I will typically make a run of 3,4,5, or even 6 beers, each with increasing sugar content in order to make stronger beers of a certain style. Originally I did this under the surmise of higher yeast populations being able to digest the higher sugar content worts as found in big(ger) beers. While I had no idea as to why there would be different populations after 3 or 4 brews, this article fully explains the causes and reason for the heterogenicity of yeast cultures in the medium after several generations. Mutations are a normal variant of yeast reproduction, and can be demonstrated in a home brew setting within a very short period of time. It’s interesting to point out that it’s the mutative feature of yeast that allows for this phenomena to occur, elsewise we wouldn’t be able to grow up enough ethanol tolerant yeast to make some of our favorite beer styles such as Barleywines, and Russian Imperial Stouts! Since I brew a lot of Belgian style beers, it was of necessity that I brewed this way so I could get not only the traditional level of alcohol as found in these styles of brews, but also to make them dry enough to be as drinkable as possible. This might also explain why historically we see beers increasing incrementally in intensity as the wort composition increases in gravity. One experiment I have done, and encourage everyone else to try is to make a series of beers within the same family of beers, slowly increasing the original gravity with each successive brew. Then compare these beers to one made with a sufficient quantity of active healthy yeast for fermentation to finish the beer to its terminal gravity. My results always showed that I got better results by using the aforementioned method of increasing wort gravity over a simple single brew made with adequate yeast. Apparently the mutating yeast account for the difference, and makes for a more complex, and therefore superior beer in my humble opinion. Let me know in the comments section what your results are and I’ll publish a tabulation of those results here for everyone’s benefit.

Fermentation Chart

Notice the decreasing return on ethanol production with increasing sugar content in this graph. Very typical of a homofermentive population.


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