Christopher S. Wood, PhD
Wild Yeast Fermentation
Recently I made an acquaintance with one of the founders of South Yeast Labs, a startup company in South Carolina that harvests wild yeast from objects in the environment like fruit, bee hives, and even brewers’ beards! The group at South Yeast Labs cultures these wild yeast, tests their ability to ferment sweet wort, and sells them to homebrewers and commercial breweries. Since making an acquaintance with the fellas at South Yeast Labs, I have used their yeast in my homebrews making them a lot more “wild.” Because there are so few published resources on brewing with wild yeast I am going to use this post to provide some basics on brewing with these wild beasts.
When I think of wild yeast I think of Brettanomyces (also known as Brett), a close cousin to the more domesticated brewer’s yeast Saccharomyces cerevisiae. In addition to Brett there are also many wild species of Saccharomyces that exist on the skins of fruit and other places in the environment. Under normal circumstances, wild yeast in a beer is considered a contaminant, but more recently some homebrewers and professional brewers have used wild yeast intentionally with amazing results.
The flavors and aromas that Brett and wild Saccharomyces yeasts can produce are very different. Brett characteristics can be described as “horse blanket,” “barnyard,” “earthy,” and “funky,” while wild strains of Saccharomyces tend to add “spicy,” “leathery,” “estery,” and much less funkiness to a beer (although results will certainly vary between strains, fermentation temperature and pitching rate). One major difference when fermenting with wild yeast compared to domesticated yeast is that fermentations are much more unpredictable. Let me explain…wild yeast tend to not settle out as much (they have a lower flocculation), and produce a higher attenuation leaving beer very dry (likely because they consume a wide array of long and short chain sugars unlike their domesticated cousins who break down mostly short chain sugars). When using wild yeast one common thread among well-respected commercial brewers is that they should be double pitched similar to pitching a lager strain since they tend to work much slower than domesticated strains. I have brewed with wild species of Saccharomyces on many occasions and in my experience the fermentation is less vigorous and lasts much longer (around a month of consistent fermentation) compared to less than a week for domesticated yeast. With even longer fermentation times, most Brett strains can take anywhere from 5 weeks to 5 months to reach peak growth! Brett also requires approximately a quarter of the oxygen that Saccharomyces yeast does, so too much oxygen can cause vinegar-like off flavors. These are just a few examples of how wild yeast can add distinct characteristics to a beer.
I hope this post has shed some light into the wonderful world of wild yeast. Up next I’ll post some interesting results from my latest homebrewing exploits with wild yeast. Until then, make sure you head on over to Richard Bolster’s “New to Homebrew” blog to learn more about our collaboration brew using wild yeast in a saison.
Happy wild brewing scientists.Last modified on