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Sour beers are stepping into the spotlight, and what was once a niche type of brew is enjoying some fresh popularity. If you haven’t tried your first sour beer yet, know that “sour” is serious--some of these can be as mouth-puckering as sour candy, or have a gentler, lemonade-like tartness. Luckily, some of the best sour brewers are here in the Bay.
Sour is more a a descriptor than a style, an umbrella covering a wide range of flavors with origins across the globe. For a good portion of human history, most beer was at least a little sour. Remember that microbiology is still pretty new, and breweries didn’t pinpoint the yeasts and bacteria responsible for spoiling beer until the 1880s. Fun fact! These are the same yeasts and bacteria that make sour beer sour.
Non-sour beers are fermented by brewer’s yeast (saccharomyces if you’re fancy), and brewers work to keep all other organisms out of the brewing process. If they’re making sour beers, however, they willingly bring in three organisms known for ruining beer--brettanomyces, lactobacillus, and pediococcus.
Brettanomyces is a wild yeast that lives everywhere. Seriously, everywhere. The surface of fruit, the nooks and crannies of barrels, and even your skin are all home to brett. Though it can create some pretty rough barnyard-esque aromas, when properly cared for brett is behind the delightful earthy funk in Belgian style sours and saisons. Brett alone won’t make beer sour, but when combined with bacteria or acidic fruits it will add depth and complexity to tartness.
San Leandro brewery Cleophus Quealy’s tart, barrel aged saisons like Batch 43 / Blood Orange Saison (5.5% ABV) or Batch 47 / Plum Saison (7.6% ABV) get their funk flavors from brettanomyces, which also eats up excess fruit sugars to give these farmhouse ales a dry, wine-like finish.
Lactobacillus is actually a bacteria, not a yeast. It produces the lactic acid responsible for the acidic bite and in tarter beers. German-style sours are soured only with lactobacillus, typically added in the early stages of brewing instead of during fermentation and aging. This process, called kettle souring, creates the clean, bright tartness in Berliner weisses, like Drake's Brewing’s Oaklander Weisse (3.8% ABV).
And then there’s pediococcus.
Some sour brewers skip this bacteria because it can get real weird. Pediococcus is the same bacteria that puts the “sauer” in “sauerkraut,” and it can contribute similar flavors to beer. It also has the potential to produce viscous, slimy chains of starches. However, brett can easily break down the ropey strands, leaving lactic acid tartness and funk that lactobacillus can’t create by itself. It’s rare to find a sour beer made only with pediococcus--it’s typically combined with lactobacillus and brettanomyces, especially in contemporary American sour or wild ales.
Renowned sour brewery The Rare Barrel in Berkeley uses pediococcus, brett, and lactobacillus to ferment their sour Map of the Sun (5.3% ABV). The rounded tartness of this apricot golden ale comes from all three organisms working in tandem to create sharp lactic acidity, barnyard-y funk, and complex fruity flavors.
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