Sour beer is the hottest cold drink of 2017. The funky brew is the latest niche offering to take off in a market obsessed with finding ever more obscure and complex beers. In recent years, craft beers have soared in popularity, with particular varieties, such as extremely hoppy IPAs, gaining a strong following among a cadre of beer drinkers, who increasingly view beer with the discernment, vocabulary and sophistication once reserved for wine.

Portland’s Ecliptic Brewing introduced a peach sour beer last year and saw sales of the brew double this year, spurring the brewmaster John Harris to make a new batch every week rather than every other week. The soft flavor of peach found such a large following that the brewery decided to make the sour beer — typically seen as a summer drink — all year round.

“Thirty years ago we would have thrown these brews away, saying they were bad,” Harris says. “Now, we are purposely putting tanks in our breweries to sour beer. It’s the evolution of craft brewing now.”

And it’s not just Portland. Sour beer has become a go-to for craft breweries across the country, as sales have spiked. Just 45,000 cases of sour beer were sold in the U.S. in 2015, a figure that more than quintupled to over 245,000 cases in 2016 and is set to rise an additional 9% this year, according to Bart Watson, chief economist at Brewers Association, which supports the American craft beer industry.

Sour beer is still dwarfed by better-known craft brews, such as IPAs, which sold 14.5 million cases last year. But it’s become popular enough for major chains to take note. Whole Foods now carries sour beer from more than 150 different breweries, and beverage category manager Joe Kaulbach says sales are up 25% from 2016. Anhueser-Busch InBev, which makes Budweiser, also owns smaller breweries that make sour beer, including Long Island’s Blue Point Brewing Company. At MillerCoors, Blue Moon sometimes makes makes sours at its Denver brewery, but they’re just for visitors to try on tap and haven’t yet been packaged and sold.

The taste of sour beer may be exotic to American palates, but the beer’s flavor actually dates back to the early days of brewing, when beer came only in an unpasteurized form, teeming with bacteria. The drink gets its tart taste from bacteria like Lactobacillus and Pediococcus, which produce acids that cause it to sour.

While sour beer’s flavor is old, American brewers have only learned how to safely produce it en masse over the past five years. Conventional beers are brewed with a single strain of yeast to yield the same taste in every batch. Sour beer, in contrast, uses a variety of bacteria and wild yeast, which can produce a different mix of flavors each time, ranging from spicy and leathery to fruity and floral. The process is tricky to perfect — one rogue microbe could potentially infect an already-sterilized beer, causing it to ferment further than intended. Most American brewers avoided sours for fear of losing money on the fickle brew, says Matt Miller, 34, a home brewer since 2011 who will open a sour beer-focused brewery called Mellow Mink Brewing in Mechanicsburg, Pa. next year.

After years of experimenting and sharing tactics, though, many brewers have now perfected the processes to produce enough of the brew to keep up with growing demand, Miller says. Across breweries that produce it, sour beer is quickly outselling other forms of craft beer like pilsner, stout and lager, with sales second only to IPAs, according to Miller and other beer makers.

“The science and research and communication that have now become available online has made a lot of the mysteries and questions of why things are less consistent easier to tackle,” Miller says. “Brewers are learning to make sour beers so there’s less waste and better consistency of product.”

Sour beer comes in many varieties, which have been refined over the decades in Germany and Belgium, where sour beer has long been popular. There’s the light and tart Lambic beer, the fruity Flanders brew, the sea salt and coriander-influenced Gose and the lemony wheat beer Berliner Weisse. In the U.S., beer makers often put an American twist on the traditional recipes, with the addition of fruit or other ingredients to draw out tart and sweet flavors.

According to Dan Jansen, brewmaster at Blue Point Brewing Company, sour beer has become a phenomenon because it gives beer fans something new to try, while also enticing people who don’t think of themselves as beer drinkers. Sour beer is comparable to wine in its method of preparation — both are blended and can be aged in oak barrels — and in the way it balances sweetness with acidity. Much like wine, the drink also pairs well with the cheeses, meats and fruits you might find on a charcuterie board.

“You can draw in a lot of wine — or perhaps certain kinds of cocktail — drinkers who may not be beer fans,” Jansen says. “It’s a whole new spectrum of beers they might not have thought existed before.”

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Write to Mahita Gajanan at mahita.gajanan@time.com.