What Is Brettanomyces, The Yeast That Makes Beer Sour?

Brettanomyces — or Brett — is the type of five-syllable word that tends to make even the most curious stop reading. Please don’t. For the wine lover, Belgian beer fan, or just adventurous drinker, big bad Brett is a necessary addition to your drinking vocabulary.

In nature, Brett resides on the skins of fruit. In wine, Brett is almost always a negative attribute, leading to “Bretty” flavors that you’d send back to the kitchen. And for the majority of beer, it’s something that’s battled against like the enemy. But as the craft beer industry in America has matured and become more reflective of the palate found abroad, Brett has started showing up in breweries across the country, this time intentionally.

Brett was first discovered and classified in 1904 by N. Hjelte Claussen at the Carlsberg brewery, after the microbe spoiled some English ales. However, the definition of “spoilage” is relative. For Carlsberg’s brewer, and most craft brewers today, any unwanted yeast or bacteria leads to inconsistent products (I recommend opening any Brett bottles near a sink due to foaming problems) and flavors that are far from popular among most consumers.

But when handled correctly, Brett produces some of the most interesting flavors available to a beer drinker. This is especially true if showcased in conjunction with Lactobacillus and Pediococcus, where it plays a funky tune next to sour and tart flavors.

Along with being hard to manage and predict, brewers also need a dedicated system for the Brett beers (so as not to cross-contaminate) and will often age the beer in oak before bottling, adding to the cost. So expect the beer to be funky and costly. But with characteristics that are often associated with the fruitiness and acidity one might find in wine, or more world-renowned lambics that have been brewed for a long time in a country far, far away (Belgium), Brett is coming back into the fold of American brewing.

If this brief intro to Brett piques your interest, check out this piece from The New York Times.