Upslope Brewing got its start five years by focusing on traditionally-styled beers that it packaged in cans. Since then, the Boulder brewery has grown both in size -- it now has two locations -- and in scope, making some huge, Colorado-style beers.

Crooked Stave started four years ago with a singular goal of making wood-aged sour and wild ales that challenged palates and style guidelines. Today, the brewery is a nationwide cult favorite with a showpiece tasting room in Denver's hippest neighborhood.

See also: Upslope follows up big new brewery with a huge new beer, Imperial IPA

"We are on different ends of the beer spectrum for sure," says Upslope head brewer Alex Violette. "But we both love each other's beer."

Which is why the two breweries have put together an unusual collaboration called Ferus Flexus that will debut at Upslope's Lee Hill taproom during a party next week and then will be sold exclusively from the taproom in 19.2-ounce cans.

It will be the first collaboration in a series that Crooked Stave is planning to do with a variety of different breweries, according the company's website.

To make Ferus Flexus, Violette started brewing a batch of Upslope's summer seasonal, Belgian Pale Ale -- but before he added any yeast for fermentation, Violette gave some of the wort to Crooked Stave and took the rest for himself. Each brewery then added a strain of Brettanomyces yeast; Upslope aged its version in red-wine barrels.

"It's not sour so much as it is wild," Violette says of the flavor. "The Brett really dried out the beer, and also made it really fruity. There's a lot of mango and pineapple coming out. I'm excited, and excited to put a wild ale in a can."

Crooked Stave's planned series of collaborations "will allow us to work alongside fellow brewers to showcase the contrast that occurs from fermenting with Brettanomyces," the brewery says on its website. "The concept for this series came about after many late-night discussions while drinking beers fermented with Saccharomyces, and the curiosity behind what these beers would taste like with Brett."

On Monday, February 17 at 6 p.m., Crooked Stave will begin selling bottles from its taproom for $10 with a four-bottle limit; draft pours will start at 6:30. Upslope will host its own release party the next day at its Lee Hill taproom at 6 p.m.; 19.2-ounce cans will cost $14 with a three-can limit. There will be a food truck on hand.

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