ASHEVILLE N.C.— Peter Batinski emerges from the depths of Hi-Wire Brewing’s South Slope taproom wearing thick black rubber boots and goggles that hold back a shock of brown hair from his forehead. Vapor rises from one of the silver cauldrons in the back, and the brewer sporadically checks over his shoulder to ensure the pot’s contents stay contained. The vibe here comes across as a bit mad scientist, and perhaps it should — Batinski is experimenting on a wild creature.
The beast in question is a yeast: brettanomyces, commonly abbreviated to “brett” by the brewing community. Traditionally regarded as a wild contaminant of beer crafted with domesticated saccharomyces yeast, brett has begun to attract Asheville-area brewers looking to spice up their offerings with unique flavors. “For me, it’s a new adventure,” says Batinski. “I’ve been brewing for over a decade, but this side of it is a whole new world.”
The key to brett’s appeal, explains Burial Beer Co. lab director Rachel Simpson, is its ability to alter previously inaccessible parts of a beverage. “Brett can ferment complex sugars that saccharomyces just can’t, and thus keeps chewing through sugars in the bottle to create an ever-evolving product,” Simpson says. Because brett breaks down the sugars left over from domesticated yeast over time, the same beer can have a completely different profile after a few months compared to its taste when first drawn out of the barrel.
Brett is also invaluable when brewing sour beer styles such as lambics and Flanders red ales. The yeast isn’t directly responsible for those beers’ tang; that’s the job of lactic acid bacteria such as lactobacillus. Instead, brett smooths out the flavors left behind by enthusiastic bacterial activity. “Many of the compounds made by lactic acid bacteria are undesirable to most people, but brett can metabolize them easily into various other things,” says Simpson. “If you get a perfect marriage of the right strains, the results can be magical.”
The flipside of brett’s versatility, however, is the equally wide range of chemicals it can produce, not all of which are quite as magical as desired. Brewers prize the spicy and fruity flavor compounds they can coax out of brett, such as tropical ethyl caparoate and applelike ethyl hexanoate. But the yeast’s historic reputation as a problem comes from its phenols, which are often described with terms like medicinal, barnyard or even sweaty horse blanket. Another brett product, isovaleric acid, is responsible for the funky aroma of Swiss cheese — and foot odor.
No strain, no gain
The first step to reining in brett’s flavors is taking it in from the wild. Brettanomyces is actually a genus of yeast, comprising at least four species, and different varieties contribute to brewing in vastly different ways. Determining an appropriate strain can be the work of many years, as it was for Zebulon Artisan Ales owner and brewer Mike Karnowski.
“I’ve been using brett as part of a mixed culture since the early ’90s, but the real focus started a year or two before I opened Zebulon,” says Karnowski. “Finding my favorite brett strains to use at the brewery meant trying almost every strain commercially available — I had dozens of these experiments going.”
Once a brewery arrives at a successful strain, it can maintain the yeast in much the same way as a sourdough starter for bread. Hi-Wire’s Batinski uses a house strain that originated over a decade ago with John Parks, now with Zillicoa Brewing. “Essentially, I just keep it in a room-temperature solution, and every other time I brew, I top it back up with wort,” Batinski explains.
Other brewers, including Karnowski, take a more regimented approach in a drive for greater control over the process. “I purchase small quantities of our brett strains and build them up into a gallon starter,” he says. “After a few months, I dump it and start from scratch in order to keep the ratio of the bretts in our blend consistent.” Companies such as White Labs and Oregon-based Wyeast Laboratories maintain pure brett cultures for brewers to use whenever they need a fresh start.
Savoring the challenge
Even consistent strains of brett hold surprises once brewing gets underway. As Wicked Weed co-founder and head blender Walt Dickinson describes the challenge, “Saccharomyces is like a Labrador retriever: It’s lovable, it’s friendly, and everyone knows what it’s going to do. Brett is like a gray wolf: It looks like a dog, but it’s more unpredictable — it demands a little more respect,” he says.
Brett’s behavior can change depending on when producers add the yeast during brewing. During primary fermentation from wort into beer, for example, brett often has more room to express itself with spice and funk than it would during secondary fermentation in barrels. Temperature also plays a key role, with warmer conditions (around 75-85 degrees Fahrenheit) making the yeast more assertive.
Despite these quirks, Asheville’s brewers are excited to discover what new horizons of flavor brett might open up. “We haven’t figured brett out in the same way that we have other types of yeast,” says Batinski. “It was once regarded as off-flavored — something you didn’t want in your beer — but taste buds have changed. There’s still a lot of experimentation to really hone it in and get what we want out of it.”