Some brewers don’t realize that beer yeast, like all yeast has a limited alcohol tolerance. In fact many some beer yeasts reach their limit below 8% ABV which can be a real problem for high gravity beers.
Yeast Alcohol Tolerance
Yeast is a one cell living creature. As such it can only reproduce and grow within certain conditions. One of those conditions includes the presence of alcohol. Each yeast strain has a limit, called the yeast’s “alcohol tolerance” that indicates the level at which yeast cells start to go dormant and stop fermenting. By convention, the alcohol tolerance is expressed as a percent Alcohol by Volume (%ABV). Most major yeast suppliers do provide alcohol tolerance numbers for their yeast strains, though you may have to dive deep into the spec sheet to find it.
Alcohol tolerance varies depending on the type and specific strain of yeast. Most beer yeasts fall into the 8-12% ABV range for alcohol tolerance, though some English ale yeasts go as low as 7% and some high gravity Belgian and ale yeasts can tolerate 15%. Wine yeasts generally have an alcohol tolerance between 14-18%, though some specialty wine and Champagne yeasts can reach as high as 21% alcohol.
Alcohol tolerance is not a fixed number, as there is some variation depending on yeast strain, yeast health, nutrients and sugar available and other factors. However fermentation will start to slow considerably as a yeast approaches its alcohol tolerance level and will stop completely within a percent or two of the published number for most strains. This can be a real problem if you brew a high gravity beer with a low tolerance yeast strain, as the result will be a very high finishing gravity and overly sweet beer.
The fact that yeasts stop at a certain point is widely used in beverages like sweet and fruit meads where you want residual sugar in the finished mead. Some mead makers accomplish this by using a very high starting gravity with a known yeast, so that the yeast reaches its alcohol limit before all of the honey is consumed leaving a high finishing gravity and residual sweetness in the mead. The same can be done with fruit beers and dessert wines to create a beverage with residual sweetness to accent the fruit.
Alcohol Tolerance and ABV in BeerSmith 3
With the version 3.0 release of BeerSmith, the software now recognizes and uses the ABV limits of various yeast strains. Each yeast strain in the program now has an alcohol tolerance field you can display and edit that is also used to estimate final gravity and ABV.
For most of the major yeast producers the BeerSmith 3 yeast database has the alcohol tolerance already populated under Ingredient->Yeast. If you build a new recipe in BeerSmith 3 it will use this number to estimate the final gravity, so if your final gravity seems very high on your high gravity beer you may want to examine the yeast strain used.
Also because the alcohol tolerance field did not exist in BeerSmith 2 some users have run into problems importing recipes from BeerSmith 2. In this case the program will set the alcohol tolerance to an “average” rate of 10% for your yeast imports, but this can create problems for older recipes. If you are building or editing an older BeerSmith 2 recipe, and the ABV won’t go above 10% then this is most likely the cause and you need to either edit the details of the yeast strain you are using in the recipe or select a new yeast strain from the BeerSmith 3 list to get the updated data.
Those are some tips on understanding alcohol tolerance for your yeast in BeerSmith 3. Thanks for joining me on the BeerSmith Home Brewing Blog. Be sure to sign up for my newsletter or my podcast (also on itunes…and youtube…and streaming radio station) for more great tips on homebrewing.