“I was a beer buyer 15 years ago, and I could not sell a sour beer to save my life,” Jenna Figuerido, general manager at The Independent in Somerville explains. She would stubbornly keep trying to put Duchesse de Bourgogne, a Flanders red ale style beer, on lists and it wouldn’t sell. She was the only one drinking it.

Now it’s flying off shelves.

“It’s crazy how within 15 years something you were begging people to try because you knew it was good, and the history, and people were like, ‘It’s kind of weird.’ Now they’re like ‘Oh this is interesting!’ It’s definitely one of my favorite beer trends that has come to fruition. It’s like watching your child go from baby to graduating high school.”

Given the name, it’s not necessarily hard to understand why sour beers were initially a hard sell to skeptical consumers. But in recent years it’s become one of the most sought after and prized specialties for beer-lovers. And yet, it still presents all manner of problems when it comes to explaining its appeal to the uninitiated; namely, it’s kind of hard to succinctly explain what a sour beer actually is.

Yes, there are common factors, and emblematic styles, most of which, like lambics, geuze, and Flanders red are Belgian, but even talking to a number of local brewers who work with sours themselves, the vastness of the category, and the potential for detours further complicates things. That’s part of the appeal for contemporary brewers, ever on the search for originality and the often unique discoveries that make brewing part science and part successful happenstance.

In general, it’s the use of wild, or non-traditional brewers’ yeasts in the process that make sours, or wild ales, a category that often overlaps, such a thrill. Unlike in modern brewing methods where specific, isolated yeast strains are used in a controlled, sterile environment, sours might do one of a few things: mimic the Belgian tradition, where ambient yeast from the environment — literally leaving the window open and letting fall what may into the mix — or working with Lactobacillus, Brettanomyces, and Pediococcus. Others might introduce fruits into the recipe to enhance or highlight specific tart or sour notes.

“The short answer, honestly, is just a beer that’s sour,” Louie Berceli of Mystic Brewery in Chelseaexplains. “It’s sort of a catchall term for a lot of differernt styles, some that actually aren’t that acidic. I think it was regionally used as a way to help Americans wrap their heads around it.”

Contrary to what you might be thinking if you’re unfamiliar with sours, it’s not an innovation, but rather a throwback. It’s likely that all original beers were sour to some extent. Mainly, Berceli says, “because sour beers more often than not are using wild yeast and bacteria.” The mass production style we know today wasn’t exactly available to 12th century Trappist monks.

A bottle of De Varenne.
The De Varenne's funky flavors come from wild yeast and aging in multiple barrels for at least a year.
Courtesy of Mystic Brewery

Wild yeasts are the connecting thread for most sours. In Belgian styles, there might be thousands of different yeast strains and microorganisms at work. Elsewhere you’ll find Flanders reds, a darker, wine-like, almost tart grape style or a German Berliner Weisse, using the Lactobacillus bacteria. The flavors here will be somewhat cleaner, sour, and acidic. The German gose style typically uses coriander and salt, for a slightly sour, clean acidity.

Brettanomyces is a key component in the sours they’ve worked with at Mystic, a yeast that adds a complex, earthy, “barn yard” flavor to beers, the types of things you’d find in a soft cheese. That’s what you’ll find in lambics and the more complicated Belgians. That’s not something easily replicated in the more urban environs of an American brewery, which is why goes and Berliner Weisse are more typically favored by Americans. “We can’t just open our windows, we don’t have the same type of yeast,” Berceli says.

The sours on offer at Mystic and other local breweries tend to be seasonal and short runs — as the process is lengthy and unpredictable. That means they also tend to be more expensive than a beer neophyte might be used to paying. A recent release was their Letters After Z, a saison farmhouse, dry-hopped sour ale using Lactobacillus. The result was akin to fresh-squeezed grapefruit, with bright citric acidity and a touch of lychee.

Barrels at Mystic Brewery in Chelsea.
Mystic Brewery in Chelsea focuses on Farmhouse style beers, using fermentation to impart distinct New England flavor. When you are using native wild yeast, you get a true taste of place. (Photo: Courtesy of Mystic Brewery)
Courtesy of Mystic Brewery

In the coming months they’ll be releasing another sour per month, using different types of hops and acidity levels.

Lactobacillus plays a significant role in the sours they’ve produced at Night Shift Brewing in Everett, co-founder Michael Oxton says. The chief result is a beer with a higher level or acidity and tartness. Their most successful sours to date, however, have been Berliner Weiss styles utilizing different types of fruit, like the Ever Weisse aged with strawberries, kiwis and hibiscus. New beers will be rolling out soon, and some are available at their tap room now.

“I would say it’s totally different than any traditional beer that most people have had,” he says of the appeal. “A lot of people come in and taste sour for the first time and don’t believe it’s beer. That’s a combination of using fruit and Lactobacillus, you get this really tart, acidic flavor profile, something that tastes completely different than an IPA or lager.”

Outside of tap rooms, you’ll find a wide array of sours at bars like Lord Hobo, Publick House, and theTip Tap Room, or on Figuerido’s bar at the Independent.

“We always have Duchesse on because it’s a classic,” she says. Also on offer at the moment is Tartare Rouge from Bear Republic, a sour red ale made with airborne wild yeast and bacteria from Sonoma County, and The Sauer Peach from Sloop Brewing in New York, a Berliner Weisse style fermented with peaches. She calls it a beautiful marriage of sour and sweet.

Contrary to the name, these aren’t the type of sour you might be thinking of.

"I think when they hear the term sour people automatically think of sour candy,” she says. “It's just going to explode in your mouth. It’s like that but not. It’s not going to make you pucker in that overly sweet taste. It’s a refreshing sour beer.”

As the spring and summer approaches, it’s a great time to reach for a sour, Berceli says, particularly one using Lactobacillus. “It’s the perfect warm weather drink. You’re getting a slight acidic tang like you get in lemonade, and more often than not lower alcohol content, and refreshing.”