Mixed-Culture Fermentation Stretches The Boundaries of Beer

Break a down beer to its essential components—barley, hops, water and yeast—and it’s easy to see how tiny variations in each can alter the flavor of a finished brew. In the case of yeast, a single strain is all it takes to transform barley and hops into beer, and most traditional recipes are made with yeasts cultivated in labs that can help brewers achieve predictable results.

So when the brewers at Woods Beer Co. in San Francisco discovered that a batch of their Bohemian Pilsner was unexpectedly infected with a rogue strain of Brettanomyces C in addition to the traditional lager yeast, it was initially an unwelcome surprise. But instead of throwing out the entire batch, head brewer Sam Bennett says they realized the flavors of the mixed-culture brew actually tasted good, so good that they decided to try to replicate it, this time intentionally introducing the secondary Brett yeast to the mix to see if they could achieve similar results. “We’ve brewed this beer two or three times since the infection happened. It’s a crisp, refreshing lager with notes of hops and grain but with an undertone of peach,” he says. “It was a beautiful accident.”

Unlike with spontaneous fermentation, which happens when brewers allow ambient or wild yeasts to run amok in a beer (i.e., what happened with the first infection at Woods), mixed-culture fermentation differs slightly in that brewers intentionally select a combination of different yeasts and bacteria to work their magic in a fermentation with the goal of creating something new and interesting. “More brewers are taking a leap into this world of mixed fermentation, and it’s becoming more popular because people are always looking for something new—especially in craft beer,” says Bennett. “There are new flavors to explore, new interactions between yeast and hops and a never-ending world of flavor coming out of this process.”

“When you have a mixed culture, you get more complexity in your flavors,” says Jonathan Williamson, of the soon-to-launch Sandhills Brewing in Kansas City. “That doesn’t mean better, just more complex. You can find fruit, acidity, and barnyard flavors like hay and blanket, which sound offensive but they’re delicious.”

At Athens, Georgia-based brewery Creature Comforts, wood cellar and specialty brand manager Blake Tyers and crew have experimented with the process in many of the house beers, including The Curious No. 2. Made with a layered mix of standard lager Saccharomyces, wild Saccharomyces, Brettanomyces, Lactobacillus, and Pediococcus, the beer won a bronze medal at the Great American Beer Festival in the American Brett category in 2014 for its exceptional balance and personality. “Many of my favorite drinks or food have flavor profiles that express some combination of bitterness, acidity and sweetness,” Tyers says. “Mixed fermentation ultimately leads to a much broader spectrum of what’s possible.”

“I’m taking a blend of flavors, a concept, and an idea and working it through the aging and maturation process to achieve what is a loose vision of what I set out to create,” says Wicked Weed head brewer Walt Dickinson of the mixed-fermentation process. “There’s a point where sometimes the yeast will push me in a different direction that I didn’t know I’d get to because that was just part of the evolution. It’s like creating a piece of art.”

That element of surprise means results don’t always come out as planned, but for brewers like Dickinson, part of the appeal is relinquishing control and seeing what happens. “Look at where beer was 20 to 30 years ago—domestic beer was like selling socks. Which pair of socks do you want?” says Dickinson. “[Mixed-culture fermented beers] are different way of thinking about how to produce a product. You have an idea of what the end product will be, but it’s through the development and artistic process that you finally reach what it turns out to be.”

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