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Craft beer drinkers generally like to know what they’re drinking—just ask the guy who won’t rest until he learns exactly where the malt for his nut brown came from.

But if you’re into sours, there’s a pretty good chance you actually ��Dz�’t know what you’re drinking. “Sour is a perception. It’s not a style or a process,” says Lauren Limbach, wood cellar director and blender at New Belgium Brewery. She’s worked on New Belgium’s sour program for 20 years and knows the genre better than almost anyone else. Limbach explains the problem like this: If a brewer adds passionfruit to an ale, the result may make your lips pucker. Technically that counts as a sour beer. But it’s worlds away in taste and nuance from barrel-aged, bacterially fermented sours, which take months to produce and have more in common with a fine white wine than a fruit-shocked wheat beer.

This spectrum of sour beer–producing techniques also leads to a range of prices that can be mystifying for the uneducated consumer. Limbach wants to alleviate some of this confusion, so she and several colleagues from breweries specializing in fermented sours are forming the (SWAG). The guild is in its infancy, but since you need to be able to choose a good bottle of beer tonight, we asked several soon-to-be SWAG members to elaborate on the “fake” sours to avoid and the best “real” sours to drink.

What Makes a Beer Sour?

There are a few ways a brewer can add tang to their concoctions. The cheater’s method is simply to spike a brew with lactic acid. While Limbach is loath to call any sours unworthy, these she does despise. “It’s really cutting corners,” she says, and the results generally show it. Beers that have food-grade lactic acid mixed in tend to have a very one-dimensional sour flavor. Yes, they’re sour, but that’s about the only flavor you’ll get.

A better option is a kettle or quick sour. “For these, you either add bacteria right at the beginning or let the mash sour by letting it steep,” says Alex Wallash, co-founder of , an all-sour brewery in Oakland, California. Rare Barrel doesn’t make any kettle sours, but he’s familiar with the technique. Once the initial mix has reached the right level of sour, the brewer can finish the brewing process like any other beer. This involves boiling the mix, which kills any of the bacteria that were introduced, so it’s not a live product like a barrel-aged sour.

This brings us to the best-of-the-best option when it comes to sours: the barrel-aged, wild-fermented variety. These beers ferment slowly in bacteria-inoculated wood, where the bacteria can consume sugars and turn them into acid. The process produces esters and phenols—chemical compounds that add unique and nuanced flavors—resulting in wildly interesting beer.

So How Do I Know What I’m Getting?

That’s that tricky part. Right now, it’s the sour Wild West. “The landscape has changed so much,” says Limbach. Years ago, before sours were cool, New Belgium named its first sour La Folie, because it was such a cash-silly endeavor. But now “sales volume for sours is up seven times, and overall they’re like 1 percent of craft beer sales,” she says.

Since there are no standards in place for what constitutes a sour (remember, it’s a descriptor, not a style), look to price when trying to orient yourself. Quick or kettle sours shouldn’t be all that expensive. But a barrel-aged, wild-fermented sour will be pricey. Not only does it take years to cultivate a barrel’s ideal bacterial culture, but aging the beer takes time. There can also be a lot of waste in the process. “Twenty percent of all the beer we’ve made since opening we’ve dumped,” says Wallash of the Rare Barrel. Bacteria have minds of their own, so they can occasionally get overzealous and produce undesirable flavors. Sometimes it’s a matter of one type of bacteria taking on the lion’s share of the fermenting, while other times it’s a result of the beer being exposed to too much oxygen during the fermentation process. Early in New Belgium’s experimentation process, one batch came out with notes of “flaming goat,” says Limbach. Those barrels went down the drain.

You can also sniff out a sour by the terms used on the label. “Aged in oak barrels” or “wild fermented” are two good things to look for. If it lists the types of bacteria (like lactobacillus or pediococcus) or yeast strains (like saccharomyces and brettanomyces) it’s probably a legitimately wild-fermented beer.

Is It Supposed to Taste Like This?

Most likely, yes. Sours can be extremely dry and often taste more like wine than their rich chocolate stout or hoppy IPA cousins.

But there are nasty flavors that can end up in wild fermented beer. “One is diacytal, which gives the beer this buttery flavor. Another is ethyl acetate, which gives the beer the flavor of nail polish remover,” says Wallash. Some brewers might blend a tiny amount of beer with these flavors into a batch, so the whole beer won’t taste vile, but if you ��Dz�’t like the taste of your sour, it could be those notes subtly coming through.

And then there’s butyric acid, which can give beer notes of vomit. But here’s the weird thing: If you continue to let the beer ferment, that vomit flavor will actually mellow into ethyl butyrate, “which tastes just like pineapple,” says Wallash. “So, if we taste a beer that has notes of vomit, we actually get excited because we know that we’re eventually going to have notes of pineapple.”

There Are So Many Sours Out Right Now. Where Should I Start?

A lot of the best sours only have local or regional distribution, so ask your local beer snobs what they love. But if you can get your hands on one of these bottles—either by ordering online or by conning a friend who lives nearby into shipping one to you—do it.

New Belgium Sour Saison

New Belgium released its first sour, La Folie, all the way back in 1997, before these things were cool. Now try the brewery’s , which blends a traditional barrel-aged sour with a farm ale. It’s the best of both worlds: just a touch sour, but also full of robust yeast and champagne notes.

Anything from Beachwood Blendery

Eric Salazar, the wood-aged beer supervisor at New Belgium, says this brewery in Long Beach, California, is doing oak-aged ales right. He was hesitant to recommend a specific beer since they come and go so quickly, but is going to be a hit.

The Rare Barrel Becoming

is aged in oak barrels with the addition of jammy boysenberries. It’s plenty tart, with just the right sweet notes added to the mix.

Wicked Weed Denouement

The sour category is moving in all kinds of experimental directions, but sometimes it’s good to go back to basics and perfect the gold standard for the category. The Asheville, North Carolina–based brewery starts with a golden ale and ages it in neutral oak barrels. The result is a clean sip that really lets the funk of the brettanomyces and other wild fermenting agents shine through.

Perennial Beer Funky Wit Series

This St. Louis, Missouri–based brewery is turning out perennially good sours. Limbach says the collection, which features a Belgian-style witbeir fermented in oak barrels, is always a good bet. The brewery does Funky Wit Melon, Funky Wit Raspberry Rhubarb, Funky Wit Apricot, and Funky Wit Raspberry. All are worth trying.