Any time you wander into a brewery and find a sour on the tap list it feels like a treat, especially if you’re a beer nerd and know the history behind the type of beer you’re drinking.

So what is a sour beer?

The introduction of the sour beer harkens back to the days of Belgian monks crafting the exact type of brew at their monasteries. Technically, all beers were sour back in the beginning. And it’s all because of yeast.

In many forms of modern brewing we utilize pure yeast cultures and brew with them in a completely sterile environment, this ensures that wild yeast cultures don’t mess up the fermentation. Back in the day we didn’t have this luxury, hence sour beers.

With sours, you flip the script, and encourage those wild yeast cultures to thrive and in turn you get the sour taste. The combination of wild yeast and bacteria in sour beers is what gives the beer it’s tart and acidic flavor. Typically, Brettanomyces, Pediococcus and Lactobacillus are the ambient yeasts and bacterias used to create sour beers.

Lately, Pacific Northwest breweries have been putting out some amazing sour beers. Here are four you need to try.

Fantasia || Upright Brewing || Portland
Barrel-fermented and complex: The philosophy behind this beer is to utilize whole fruit and make effective use of the wild yeasts formed in the orchard. Fantasia is crafted using peaches and contains a 6 percent ABV, the tart ale is reminiscent of Belgian lambics.

Lacto SOUR ||Schooner Brewing || Seattle
This seasonal kettle sour exhibits refreshing and slightly acidic flavor profiles, its tartness combined with floral notes make for an exciting drinking experience. Made in the style of a berliner weisse, and has an ABV of just 3 percent, it is available as a seasonal summer beer but can be found leaking into fall.  

Plum Millie American Sour || Wander Brewing || Bellingham, WA
Millie takes on many iterations throughout the year, the fruit of choice differing with the season and availability. In addition to plum, the American sour has been brewed with apricot and raspberry. No matter which version you get, it’s guaranteed to be delicious. Millie tends to be around 4.4 percent ABV, and when it’s in stock you can buy it in bottles as well as getting it on tap at the brewery.

Pearpawsterous Northwest Sour Ale || Cascade Brewing || Portland
Sours galore. It’s hard to single in on one sour beer at Cascade Brewing, the self-proclaimed member of the Sour Revolution, brewing exclusively sour beers. The 2017 Pearpawsterous features Oregon-grown pears and Indiana-grown paw paws. The beer is aged for 12 months in oak barrels before it fills any drinker’s glass and, once poured, it is a light-gold color and tastes of pears with a bright acidity.