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Yeast and bacteria 101: Brettanomyces, lactobacillus, pediococcus

The lowdown on what yeast and bacteria actually do to your beer.
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shutterstock_245846077If you’re a fan of sour beers, you’ve definitely seen some tough-to-spell bacteria and yeast names thrown around. Brett, lacto and pedio are sort of the Three Musketeers of sour beers, producing some of the flavors that make beers distinctly funky, sour and tart. (I spotted a guy at Upland‘s Sour, Wild & Funk Fest two years ago wearing this shirt. Well played, sir.) Though people often refer to these bacteria and yeast in the same breath, it’s worth taking time to explore each on its own. I asked Michael Dawson, brand manager at Wyeast Laboratories, which supplies liquid brewing cultures, for the lowdown on what each microbe does.

To understand these three terms, though, we need to begin with the two types of fermentation: wild and single-culture. Single-culture means one strain of yeast is introduced to eat up the sugars in wort, converting them to alcohol. Sour beers, on the other hand, undergo wild or mixed fermentation, meaning multiple types of yeast and bacteria work together symbiotically to turn sugar to alcohol. Within the category of wild ales, beers can be subject to either controlled or open-air fermentation. Controlled fermentation means brewers use multiple types of yeast and bacteria, but have selected exactly which strains enter the tanks. Open-air fermentation is exactly what it sounds like: Tanks are left partially open, allowing bacteria and wild yeast to drift in naturally from the environment. This method gives the beer a sense of place; open-air fermentation is what makes some Belgian beers taste so characteristically Belgian.

Prior to the work of Louis Pasteur, the invention of modern refrigeration and the discovery of microbiology, beer underwent mixed fermentation. Most non-wild beer today, though, is fermented with a single yeast strain, saccharomyces. But it is when brewers deliberately introduce other yeasts and bacteria that things get funky, mostly through the addition of these three microbes:

  • Brettanomyces (aka “Brett”): A strain of yeast, not a bacteria, that Dawson refers to as “the wunderkind of the wild beer world.” It serves the same function as saccharomyces does: fermenting beer. But Brett works more slowly, meaning a beer that could have fermented within days or weeks with saccharomyces will take weeks, months or even years to display its full character when Brett is used. Dawson rephrases a quote from the late beer author Michael Jackson: “Saccharomyces is like a dog and Brett is like a cat. It’s a little less predictable. It’s going to do its own thing; it’s not going to come when you call it and sit when you say sit. If you can respect its individuality and suggest rather than dictate what it does in your fermentation, it can reward the brewer and the drinker.” There are different strains of Brett, each of which produces its own flavors ranging from tropical pineapple and fruity peach to the intense flavors described as sweaty horse blanket, dirt, earth and barnyard. TL;DR: Brett is the microbe responsible for funk.
  • Lactobacillus (aka “lacto”): A bacteria, not a yeast. Lacto eats up the sugars in wort and, rather than converting them to alcohol, converts them to lactic acid. This lowers the liquid’s pH, making it sour. Lacto also shows up in plenty of food fermentation, from kimchee to yogurt. It’s a relatively clean taste for drinkers, since lacto doesn’t produce much besides lactic acid. It’s responsible for the tang of German styles like goses and Berliner weisses. TL; DR: Lacto produces lactic acid, resulting in a clean, sour taste.
  • Pediococcus (aka “pedio”): A bacteria, not a yeast. Like lacto, pedio produces lactic acid and lowers pH. But all things being equal, Dawson says, many people find the resulting sourness from the introduction of pediococcus “harsher” than that of lactobacillus. While lacto produces a clean sourness, pedio can contribute other funky aromas and flavors to the mix. It gives Brett more fuel to work with, so they’re often used together. It’s the bacteria that sours beers like lambics and Flanders reds. TL; DR: Pedio produces lactic acid as well as other funky and sour flavors.

 

Author
Kate Bernot is DRAFT’s beer editor. Reach her at kate.bernot[at]draftmag.com.

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