What Exactly is Brett Brux?

If you spend time around beer these days, you’re hearing a lot about Brettanomyces and its various strains. One of these more classic strains is Brett brux, and no doubt you’ve heard it discussed with a lot of words like “funk,” “barnyard,” and “horse blanket.” But there’s a lot more to Brett brux than its funk, and it all depends on where it gets used.

First, the science. There are four primary (or at least scientifically recognized) strains of Brettanomyces: B. bruxellensis (a.k.a B. lambicus), B. anomalus (a.k.a B. claussenii), B. custersianus, and B. nardenensis. Each one produces different flavors in beer, though brux and anomalus are the two most commonly used to date.

Brett brux in long-tail form is Brettanomyces bruxellensis. It’s commonly found in lambic-style beers, which still leads many folks to believe that brux is the agent that sours a beer. That’s not true. In sour beers, bacteria (specifically Lactobaccillus and Pediococcus) are responsible for producing acids that cause sourness. Brett brux is a wild yeast, one that occurs naturally in all parts of the world, but perhaps most famously in the areas of Belgium where lambic is produced. Brux is capable of producing acid (most frequently acetic—the same that’s in vinegar) by metabolizing oxygen and ethanol, but it’s not usually responsible for the bulk of acetic production in any beer.

B. bruxellensis is a single type of yeast, but it’s really more than that: it has a family of mutations. In the same way that Saccaromyces cerevisiae (traditional brewer’s yeast) encompasses all ale strains, B. bruxellensis can provide that same kind of variation. Just like a beer fermented with American ale yeast will taste different than one fermented with a Belgian trappist yeast, so will two beers fermented with different mutations of B. bruxellensis.

While different commercially available strains of B. bruxellensis do different things, brux is most traditionally known as the species that produces the infamous barnyard character.

B. bruxellensis as a Secondary Fermenter

Brettanomyces is often used as a secondary fermenter. That is, it’s pitched after or at the same time as Saccharomyces. In these cases, the two yeasts compete. But B. bruxellensis is a slow-growing yeast, which means Saccharomyces, eating much faster, gets its choice of most of the easily fermentable sugars in wort. B. bruxellensis, then, chews on long-chain sugars called dextrins which Saccharomyces is incapable of fermenting. And as Saccharomyces eats, it produces byproducts that B. bruxellensis is able to feed on. This produces many of the trademark esters and phenols that mark a beer as “funky.”

Brettanomyces is very tolerant of—if not encouraged by—acidic environments. This is why it is so important in the production of sour beers. Low pH is toxic to Saccharomyces, but Brettanomyces can survive (and even thrive) in a lactic-heavy or otherwise acidic wort.

B. bruxellensis as a Primary Fermenter

Brux doesn’t need to be used only as a secondary fermenter, though. And while there hasn’t been a significant amount of research (or brewing) done with brux as a primary fermenter, there are some significant differences that occur. When brux has access to the easily fermentable sugars in wort, it produces much fruiter notes. While some funk may still be present, it won’t be as abundant as it is when used in secondary.

This is important because the primary house yeast at Central State Brewing is a mutated strain of B. bruxellensis that has been culturing for over a year. Over this time, it has become a quick attenuating (which in non-brewing lingo means the conversion of sugars to alcohol and CO2 via fermentation) yeast and provides fruity, tropical notes when used with hops, peppery notes with a hint of funk on drier styles, but when fermented at cooler temperatures, it provides a clean tasting and smelling beer.

It is also important to note that B. brux and Brettanomyces in general is a super attenuating yeast when used in secondary. Because it eats slowly, it will continue to eat and break down sugars long after packaging. Beers fermented in secondary with Brettanomyces will change over time, often becoming dryer and continuing to produce esters and phenols. However, when used as a primary fermenter, though it will continue to chew on residual sugars over time, it will also reach a fairly stable final gravity within a matter of a weeks.