Darwin and the Art of Mixed Fermentations

Survival of Whatever Fit

 
In the fifth edition of On the Origin of Species, Charles Darwin introduced the phrase “survival of the fittest” intending it to mean “better designed for an immediate, local environment.”

As a brewer of mixed fermentation beers, you understand the importance of getting your favorite mix of yeasts and bacteria into your creations. You want diversity, but only the diverse group that you had hand selected to do the job. Once that beer is complete, you probably want to use that same culture of amazing funk and/or sour for future beers, as well. All you need to do is harvest those dregs, and off you go with your prized mix for the next project.

Unfortunately it doesn’t work exactly like that.

You can use a single yeast strain for multiple generations and, slight mutations aside, it will just get better with the first few ferments. But for mixed fermentations, you have often have saccharomyces and brettanomyces competing in some fashion for sugars, as well as lactobacillus and pediococcus bacterias doing the same. It is survival of the fittest until the bodies/cells hit the floor. Many of the players in your vessel are making contributions, but there’s only one or two MVPs being selected to represent after the game.

That concept was new to me and it was brought to my attention by Jeff Mello, of Bootleg Biology, weeks ago and he echoed it again in his presentation during this year’s National Homebrew Conference. (Yes, I continue to struggle with calling it Homebrew Con.)

When he streaks out cultures from finished beers, there are usually only a couple of winners from the yeast and bacteria genera. In addition, most “wild” mixed cultures end up being primarily yeast because of how and when they are harvested and a smaller percentage of cultures that ending up having viable bacteria if there is yeast present. (**What’s important to remember here is that this is my recollection of what he said. If what I’ve typed here is wrong, it is my error not his.**)

That isn’t to say that all of those yeasts and bacteria didn’t have a hand in the final beer, but it is a long shot that you will get the same results with those dregs in your next beer.

Does that mean commercial mixes of twenty brett strains in one vial is just a marketing gimmick? In my opinion, yes. But I have used those cultures with great success, so it is hard to dissuade you from using them, and that is certainly not my goal here. Having said that, if you know only one or two strains will shine through, it seems more logical, albeit maybe less economical, to choose those strains yourself rather than hope they emerge from the hunger games of pitching all the bretts.

What does this mean for my beers?
 
The implications of this, at least for me, was a reminder to continually push for diversity in my beers. At onset of a new batch or new barrel, I’ll still be carefully adding the commercial cultures and dregs that will create the complimentary effects I want imparted into the beer. That’s the same.
 
What might be the larger reminder is to keep pushing for diversity in subsequent generations of beers with that original culture and/or with your wonderfully funkified barrel. While brett might have crawled into your wood and your barrel is riddled with pediococcus, you still need to feed the diversity and to keep your beers from devolving into simplicity. Keep putting your favorite dregs into your beers for diversity’s sake, but also to ensure what you have what is best designed for that immediate, local environment.

TL;DR

The diversity of yeast and bacteria that you add to a beer is a continual endeavor. Your mixed fermentation beer is a living thing, and the cultures that made the beer what it is are not necessarily the ones left to harvest and repitch.

Sour Collab Barrels at a Local Brewery

Sour Collab Barrels at a Local Brewery

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