Making Darwin Proud
It’s one thing to isolate a single yeast cell in a laboratory setting, but it’s another thing entirely to repeatedly use that isolated yeast strain in the brewhouse and maintain a consistent ferment batch to batch. Eventually the resulting beer will start to noticeably change. Perhaps no one appreciates that continuous struggle better than Chris White, President of White Labs Inc. and co-author of the textbook Yeast. White noted, “It’s one of the things that makes what we do important.” White Labs handles 50 to 100 strains each week. Hundreds more are maintained in longer-term storage.
“It was historically difficult to keep yeast from changing,” White added. “If you look at how yeast storage used to be – storing it on plates and slants, so that it’s slowly growing – it will change in months of time. Storing it cryogenically is the best way to have it not mutate, to have it not change. So you have to store them cryogenically, and that’s a great permanent bank, but you have to go back to that bank regularly.”
Pick one: (a) witness evolution, or (b) freeze the little buggers.
Even in controlled environments, setting loose a pure-culture yeast strain (progressively bred from one isolated cell of the desired yeast variety) to ferment a complicated solution in varying conditions brings about an entirely new set of disorderly influences. Not all of the yeast cells will complete the fermentation of a batch in similar health, small probabilities of mutation become a non-trivial concern when yeast pitching rates are measured in the billions, and even the greatest vacuum in the world isn’t going to prevent wild yeast and bacteria from hungrily trolling the perimeters of one’s fermentation vessels. Uninvited participants can start changing the pH and kicking out off-flavors, competing for the same sugars that were intended for that original yeast strain, and soon one’s delicious pale ale recipe is tasting like bad lambic. The road to being able to repeatedly brew with a particular yeast source is, in other words, a mycological minefield.
In the past (and today, though to a considerably less degree), breweries that observed their yeast strains going off the deep end and progressively performing differently during fermentation would typically pop over to a neighboring brewery to replenish their supply – which, again, up until the last hundred years or so was determined by the microorganisms floating in the local air, instead of by what they’d ordered out of a catalog. (This would eventually be known as a “house yeast” or “house character,” as it would be specific to the individual brewery(ies) and often quite distinct.) Most commercial brewers today, whose livelihoods depend on their ability to produce a consistent product, still face a similar decision: control your yeast, or find someone who can.