This week I take a look at the concept of mixed yeast fermentation – using more than one strain of yeast to brew your beer as well as some of the strengths and pitfalls.
Mixed Yeast Fermentation History
Thanks to modern science, most of us use a single strain of yeast when we brew our beers. The vast majority of beer yeast sold commercially contains a single isolated strain of yeast cells, and yeast labs go to great lengths to ensure their yeast packs are pure.
Historically, however, things were not so simple. Before the invention of microbiology, which happened in the late 1800’s, there were no methods for isolating single yeast strains. While some breweries did self select strains by repitching yeast over and over again, the science and techniques were not well developed. So, in fact, it is very likely that mixed yeast strains along with some wild yeast strains were the norm for much of brewing history.
Mixed Yeast Strengths and Weaknesses
After 100 years+ of brewing with isolated single yeast strains, brewers are rediscovering the joys of using more than one yeast. To do so we generally pitch equal quantities of two different strains of yeast. Here are some of the strengths and weaknesses of doing so:
Strengths:
- Blended Flavors: A yeast mix tends to provide a blend of the characteristics of the two selected yeasts. So, for example, using an English Ale yeast along with a California Ale yeast will give a beer with much of the complex esters and diacetyl of the English yeast but it will also likely have the high attenuation and lower finishing gravity from the California yeast.
- Stronger Attenuation or Flocculation: If you need to finish a beer faster, you can mix a lower flocculation yeast with a higher flocculation one. What will happen is that the higher flocculation yeast will form clumps of yeast and take the lower flocculation yeast with it when clearing. Similarly a higher attenuation yeast will ferment to finish resulting in a lower finishing gravity.
- Unique Character: Blending yeasts will, quite simply, create a mix of flavors you can’t get from any single strain alone. So your beer will be unique!
Weaknesses:
- Domination: While it is unlikely with equal volume pitches, it is possible for some yeast strains to dominate other strains. This could in some cases produce undesired off flavors rather than the flavor blend you are shooting for.
- A Bad Mix: Some flavor combinations may not be complementary, and you could end up creating a combination of flavors you did not intend.
So is it worth the risk? I think so. I had Dr Chris White on my podcast to discuss mixed yeast and he said that in their experiments the problem of one yeast dominating another was very unlikely and in fact the vast majority of mixed yeast beers they have made came out great. He also said that they have not had any issues creating yeast starters with more than one strain.
So give mixed yeast fermenting a try – just pick two of your favorite strains out and use them in your next batch! I hope you enjoyed this week’s article from the BeerSmith Home Brewing Blog. Please subscribe for regular weekly delivery, and don’t hesitate to leave a comment or send this article to a friend.
