Sour beer is an umbrella term for many different beer styles including Gose, Berliner Weisse and Lambic. All these styles have one unifying feature: an intentionally acidic, tart or sour taste. Traditionally breweries would allow the wort to cool in large open vessels and wild yeast strains and bacteria would infect the beer and initiate fermentation.

These days certain strains of bacteria and yeast are used by breweries to intentionally sour beer. The common ones are Lactobacillus, Brettanomyces (Brett), and Pediococcus. Often you will hear people refer to these beers as containing funky, barnyard notes.