The Many Faces of Brett: Overview

Why do we go out of our way to label something as “Brett-conditioned” or “100% Brett-fermented”?

Dave Carpenter Jan 21, 2015 - 6 min read

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Maybe you’ve tasted it in a sour ale. Perhaps you’ve detected it in a unique Trappist ale. Or maybe you noticed it in one of your favorite brewery’s newest experiments. If you taste something funky, there’s a good chance Brettanomyces is showing one of its many faces.

Brettanomyces, whose name comes from the Greek word for “British fungus,” was first studied as a spoilage yeast. Winemakers the world over go to incredible lengths to get rid of it, and until very recently, so did most brewers. But now pros and homebrewers alike are taming this so-called wild yeast and inventing new styles that have about as much in common with mass-market beer as today’s HDTV does with the very first cathode ray models of the 1930s.

What’s So Different about Brett?

Strains of Brettanomyces are ubiquitous. They live all around us, not just in the Senne valley of Belgium, but on our fruit trees and in our homes. So why do we go out of our way to label something as “Brett-conditioned” or “100% Brett-fermented?” After all, Sierra Nevada’s labels don’t proclaim, “Proudly fermented with the Chico strain.”

We treat Brettanomyces strains specially because they produce flavors and aromas that are so unlike what most of us expect in beer. While most ale strains are described with pleasant terms such as fruity, banana, ripe mango, cloves, spicy, and stone fruit, the adjectives used to describe Brett character are comparatively grim.


Two of the phenolic compounds most closely associated with Brettanomyces are 4-ethylphenol—described as a sweaty horse blanket, barnyard, or Band-Aid—and 4-ethylguaiacol, which is often characterized as smoky or spicy. Brett strains also create isovaleric acid, which is the same compound responsible for foot odor and the putrefied cheese aroma we associate with old, oxidized hops.

The thing is, Brett is far less predictable than our familiar Saccharomyces strains. Two identical worts inoculated with Brett at different times and in different ways can deliver wildly different beers. We’ll cover some specifics in a later article, but for now, it’s enough to say that Brett truly is an altogether different animal.

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Types of Brettanomyces

There are myriad species of Brett bugs, but only three strains are readily available to most homebrewers year-round.

  • Brettanomyces bruxellensis is named after the city of Brussels and is closely associated with Orval, which bottle conditions with B. bruxellensis. This strain will deliver lots of sweaty, horsey Brett character and is available to homebrewers as White Labs WLP650 and Wyeast 5112.
  • Brettanomyces lambicus is a strain of B. bruxellensis. As its name suggests, it is closely associated with lambics, as well as with the brown and red ales of Flanders. This strain is available to homebrewers as White Labs WLP653 and Wyeast 5526, and it’s the one to go with for intense funk and sour cherry overtones.
  • Brettanomyces claussenii_ (which is a strain of the species _B. anomalus) is associated with the barrel-aged stock ales of the British Isles. It delivers more fruit than funk and creates an aroma reminiscent of over-ripe pineapple. This strain is available to homebrewers as White Labs WLP 645.

The nomenclature used to describe Brettanomyces is all over the place, and individual strains of the same species are commonly referred to as if they were different species altogether. But _B. bruxellensis, B. lambicus, and B. claussenii _are all you really need to know to get started with this versatile suite of bugs.

How Is Brett Used?

We’ll cover practical tips for working with Brett in an upcoming article. But what exactly do you do with it? The three most common ways you’ll see Brett employed are:

  • Mixed culture fermentation and conditioning. While Brettanomyces itself isn’t a souring agent, it is very commonly employed with the souring bacteria Lactobacillus and Pediococcus, especially in spontaneous fermentations.
  • Brett conditioning (secondary fermentation). Whether in barrels, bottles, or carboys, following a traditional Saccharomyces primary fermentation with a strain of Brett creates unmistakable flavors and aromas that can only come from wild yeast. This character is readily understood if you can manage a side-by-side comparison of young and old bottles of Orval. Or, for a mild introduction to Brett conditioning, brew up our Historic Burton IPA.
  • All-Brett fermentation. A relatively new topic in the world of craft beer, 100 percent Brettanomyces fermentation may be the next big thing. If you’re lucky enough to get your hands on any of Crooked Stave’s excellent 100 percent Brett creations, you’ll learn firsthand just how impressive an all-Brett fermentation can be.

In an upcoming article, we’ll cover some of the basics of working with Brettanomyces at home, including sanitation, pitching rates, and more. For more exhaustive information, be sure to check out Michael Tonsmeire’s excellent American Sour Beers, Jeff Sparrow’s Wild Brews, and Yeast by Chris White and Jamil Zainasheff.