What is Brettanomyces and What is it Doing in My Beer?

Here’s one science lesson worth the flop sweat and trembling limbs we used to get when we were asked to balance an equation or memorize terms like Avogadro’s Number and phalanges. Why is this particular lesson worthwhile? ‘Cause it’s about beer.

Before panic sets in, let’s just clarify the scary-seeming term: Brettanomyces is a kind of yeast (Brettanomyces literally means “British fungus,” but not because the Brits invented it; the stuff was discovered when a scientist was looking into spoilage of some English ales). A “wild” yeast (we’ll get to that) that can have a desirable, or less desirable, impact on the fermentation, and therefore flavor, of beer. It’s a good time to learn about brettanomyces, or “brett” as it’s known in the industry, and not just for basic drinker’s upsmanship; the stuff is showing up increasingly on the craft beer shelf.

Before we get into brett, a quick primer on yeast and fermentation: yeast eat sugar and create alcohol and carbon dioxide. There are various species of yeast, but the one most commonly associated with the production of beer is a strain called Saccharomyces cerevisiae. (Think “cerveza” and “cerevisiae,” it’s a good way to remember.) Among many other factors (hop and malt varieties, water/mineral content, fermentation temperature, etc.), the kind of yeast used in fermentation will impact the final flavor of the beer. That’s why some craft brewers cultivate specific strains of yeast and guard them like trolls under a bridge.

Get the latest in beer, wine, and cocktail culture sent straight to your inbox.
Got Brett?
Photo courtesy of Pinterest.com

But Brettanomyces (actually a genus) is a bit of a yeast maverick. So-called “wild” yeast, it’s been the scourge, and then the friend, of brewers for centuries. See, Brettanomyces grow naturally on fruit skins, which means in a brewery environment, which historically might have been very much in proximity to a farm or produce, there’s brett aplenty. Which is why back in the day, before sanitation methods were as extensive, brewers often ended up with a partially brett-fermented beer. The stuff existed in the ambient environment, and, yeast being the greedy bastard that it is, found its way into the tank of glucose-rich fermenting grains.

Why would a brewer want to protect his beer from brett? Because, unlike S. cerevisiae, the flavors you might get from a Brett-fermented beer are particularly distinctive, with an emphasis on funkiness, spice, fruit, and a bit of tartness (Brett specifically produces acetic acid). There are actually many different strains of Brett, each of which impart a different array of intense flavors, which may or may not be intentional. Say your beer gets “infected” with Brettanomyces Bruxellensis and you weren’t expecting your beer to taste like horse blanket. That might come as a slightly unwelcome surprise. (Trust us, in the right context, a little bit of horse blanket’s just fine.)

Golden Brett
Allagash’s Golden Brett/Photo courtesy of BeverageWarehouseVT.com

But the funny thing about brett, and something that’s kind of remained over the course of its usage (intentional or otherwise): you may hate it, but somebody out there loves it. Not only does somebody love it, but certain breweries are going to specific measures to (carefully) incorporate brett fermentation into their beer’s final flavor profile. Allagash ferments their Golden Brett with a “house strain of Brettanomyces.”  And the use of brett isn’t new. Beer styles like Lambic and Gueuze, Saison, and Flemish Red Ale have long depended on the funkitude of brettanomyces (if you like sour, grab a Geueze; expensive but worth the pucker).

Most modern day breweries, Belgian and otherwise, aren’t just opening some windows in the fermentation room and letting the magic happen. Because of its powerful impact and relative unpredictability (as far as yeast goes, brett is a bit microbiologically finicky), the stuff is carefully dosed into recipes. Some breweries are going so far as to do 100% brett-fermented beer—typically with accompanying lactobacillus and pediococcus, other scary science terms that basically mean “beer sourer”—while others settle for partial brett-fermentation. Your best bet to try some is if you see it on tap somewhere (and chances are, you will). Since brett can be incorporated into a variety of styles, it’s a fairly useful tool for brewers. Of course, they’re counting on the idea that you, too, will embrace the funk.