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Minnesota brewers are becoming fixated on mixed-fermentation

[Editor’s Note: This post will continue to be updated with more news on sours made by Minnesota’s breweries]

A whole new segment of Minnesota beer has turned sour. Or maybe not sour—that makes it sound like a mistake. These beers are intentionally tart and astringent, funky and wild.

“Sour beer” is an imperfect term—many brewers would consider these beers merely tart. “Mixed-fermentation” beer is more accurate, but that term doesn’t provide an instant flavor description the way “sour” does. “Wild” and “farmhouse-style” are also terms in the mix—pointing to a more spontaneous fermentation style. To make it more complicated, there’s no industry standard for how these beers are produced. All told, they defy simple categorization.

They do however have a common thread—this beer is fermented with a mix of yeasts and bacteria known to produce acids and funky flavors as they consume sugars. These microflora—often from the genera Brettanomyces, Lactobacillus, and Pediococcus—are used to ferment everything from cabbage to yogurt, from kombucha to kimchi, and now add a similar tang to several Minnesota beers. Sometimes the inoculation is short and intentional. Other times, it’s lengthy and unpredictable.

Several breweries in Minnesota are getting in the mixed-fermentation game. Some are making a one-off sour here and there. Some are building vast halls full of barrels and foudres. Even more have a program somewhere in between. Here is a brewery-by-brewery breakdown of the State of Sours in Minnesota in 2016.

August Schell Brewing Company

Perhaps the Minnesota brewery that’s most responsible for sparking interest in mixed-fermentation has been Schell’s. The 150-year-old New Ulm brewery is now on their tenth entry in their Noble Star Series of Berliner weisse interpretations. The newest, Orbital Drift, is not weisse at all—rather, dark from a bill of long-kilned malt.

“I really like the Berliner weisse style as a starting point,” says Schell’s head brewer Jace Marti. “I think you’re really only limited by your imagination and I like working within those guidelines to a certain extent, so we’re going to continue to push within that world and really see what we can do.”

Schell’s is building a new off-site brewery and taproom, the Star Keller, to capitalize on some of their most prized assets: 10 gigantic cypress foudres. Purchased in 1936, the tanks each have a 140-barrel capacity and eight are currently installed at the Star Keller. The other two have a difficult move ahead.

“The two tanks that started the whole Noble Star Collection at the brewery are getting moved probably July 30 from the brewery,” Marti says. “They’re two stories down underground, so we have to cut the holes in the roof and the floor on the main level to remove all the tanks.”

Once fully installed, the 10 tanks will give Marti an even greater deal of flexibility to create new and interesting takes on the Berliner weisse. “Something that we’re looking forward to with the Star Keller and having 10 tanks is having the option to blend different beers together to make single beers,” he says. The Star Keller is currently tracking for a September opening.

Their brewing process starts with a custom wheat malt that aims to replicate what brewers might have had in early 1900s Berlin. They execute a short mash that results in a wort with a good deal of residual sugar. Then, it’s a mixed-culture primary fermentation in stainless steel tanks, using a combination of ale yeast and lactic acid bacteria sourced from a closed, East German Berliner weisse brewery. Once the majority of fermentation is finished and they’ve hit the target acidity level, it’s transferred to the wood foudres where they pitch Brettanomyces, and where the beer ages anywhere from six months to two years.

“You’re at the mercy of just letting the beer do its thing,” says Schell’s head brewer Jace Marti. “From there, it’s pretty much sensory, checking it every couple weeks or so. I try not to test as much as possible because you can really drive yourself nuts when it’s going through its phases.”

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