In 2009, few local drinkers had ever tried a sour beer—it was a category relegated to a few specialty bottle shops that reserved a little shelf space for rare imports. A year later, after a handful of Oregon brewers found inspiration in a centuries-old European tradition, they began to produce reimagined takes on nearly forgotten styles, like gose and Berliner weisse, through a technique called kettle souring. Today, American sours have achieved mainstream success across the country in large part because of what happened here during the previous decade.

Credit one of those quality beer retailers for laying the groundwork for the sour boom. In 2006, a time when it was rare to find these beers outside of Belgium or Germany, Belmont Station hosted its first tap takeover dubbed "Puckerfest," which continues to this day. Though a pioneer in the sour movement, Cascade Brewing didn't start making the ales that have now become its signature product until 2005—seven years after it opened.

What prevents more businesses from getting into sour production is all the extra work it requires, the time it takes for aging, and the space needed for barrel storage. A lambic, for instance, which features a mixed culture of wild yeast and bacteria, takes several years to ferment and age as well as dedicated equipment to prevent the contamination of "clean beers"—those that use controlled strains of yeast.  >>

About a decade ago, a number of brewers began experimenting with a faster method to produce high-acidity batches. Kettle souring, as the name suggests, takes place in a stainless steel tank instead of a traditional barrel, and involves a lactic acid bacteria—usually lactobacillus—that's added to the unfermented liquid, lowering the pH. After the beer is held at a warm temperature for eight to 24 hours while a short lactic fermentation takes place, it's then boiled to kill the bacteria. While the method offers benefits, like a reduced risk of contaminating non-sours with funky flavors and no need for special equipment, there are also drawbacks, including a danger the batch will take on a rancid off-flavor.

One of the earlier kettle sour entries to the market was Bend Brewing's Ching Ching, an ale that looks like bright pink Champagne and tastes like sour candy. The business's former brewmaster, Tonya Cornett, now head of R&D at 10 Barrel Brewing in Bend, wanted to create a beer that would appeal to women and non-beer drinkers.

"I initially had a goal in 2009 to make an introductory beer that didn't necessarily taste like beer," says Cornett. "At the time, most brewpubs were filled with men drinking West Coast IPAs and double IPAs. I wanted a crossover that would encourage more women to look at beer as an option."

The first step to Ching Ching's development took place at the Great American Beer Festival in Denver that year. That's where Cornett sampled an early example of an American kettle sour—Southern California-based the Bruery's Hottenroth Berliner Weisse—a style she hadn't been impressed with in the past, but the beer's light base and lack of funky wild yeast flavors was striking. That prompted her to hit up other brewers for tips on kettle souring, and based on those suggestions, she developed Desert Rose, a Berliner weisse with hibiscus and craisins. Not immediately satisfied with the outcome, Cornett shelved the idea, until her assistant brewer brought in a bottle of Pom Wonderful a few months later. With newfound inspiration from the non-alcoholic, pressed-pomegranate beverage, Cornett wrote a new recipe for a kettle sour brewed with the fruit and called it Ching Ching.

"At first it was a hard sell," Cornett recalls, "because it was far from what most people considered beer, and it was pink."

The experimental rose-hued brew she had to sell out of the back of her car to beer bars eventually went on to snag a bronze medal at GABF in 2011 and then a gold at the World Beer Cup the following year.

The now-closed Commons Brewery in Southeast Portland put its own spin on the kettle sour in 2013 with Biere Royale. Head brewer Sean Burke, who now oversees the program at Von Ebert Glendoveer (page 20), had tried Ching Ching, and after learning the active souring ingredient was not wild yeast cultures but the same bacteria that gives yogurt its signature tang, he recalled a story from brewing school.

"One of the teachers was talking one day about a large brewery that kept having lactobacillus contamination at random times in their packaged beer," says Burke. "They finally figured out that one of the people working the bottling line had been eating yogurt on or near the line, and it was making its way into the final product."

That's how tubs of Nancy's Greek Plain Yogurt ended up becoming the souring agent in the black currant beer, which was a hit at the Portland Fruit Beer Festival and had both amateurs and pros racing to the dairy aisle to give the method a shot.

When the Craft Brewers Conference came to Portland in 2015, Burke was one of the speakers at a seminar packed with beer makers who wanted to know more about his innovative yogurt kettle souring technique. After the talk, dozens of articles were published about what some were calling "quick sours," and by 2016, Berliner weisses and goses were everywhere. The American sour ale had won fans in- and outside the industry. Eventually, the use of yogurt disappeared as cheap liquid and powdered lactobacillus became readily available, but "sour ale" entered the beer community's lexicon and has now become as recognized as IPA.

"I think a lot of brewers were attracted to it as a way to offer acid-forward beer without going through a longer-term aging process, and risk having living lactobacillus in their cellar," says Burke of how kettle souring changed the industry. "Sadly, I think it has distorted the view of what acid-forward can be, though. A mixed-culture aged beer and a kettle-soured beer are two very different things."

"In the end, I found it wasn't necessarily women who were attracted to this style of beer," says Cornett, who later launched the Crush series of fruited kettle sours at 10 Barrel. "I think the style bridges a gap between beer and the fruity cocktail or light wine drinker. It makes me especially happy when someone says, 'I never thought I would like a beer, but I love this one.' Anything we can do as brewers to turn more consumers on to beer is a good thing."