Sour Cultures

Sour cultures are used to create the tart acidity and complex fermentation character found in sour and mixed fermentation beers. Unlike a conventional brewing yeast, a sour culture may contain brewing yeast alongside microorganisms such as Lactobacillus, Pediococcus, or Brettanomyces, with the exact blend determining how the beer develops. Depending on the culture and brewing method, flavors can range from bright, clean citrus like tartness to deeper fruit, earth, funk, and long aged complexity. Sour cultures are commonly used for Berliner Weisse, Gose, Lambic-inspired beers, Gueuze inspired blends, Flanders Red and Brown Ales, American Sour Ales, and fruit sours, although specific cultures may be designed for either fast souring or extended maturation.

Compared with Ale, Lager, and Belgian yeast, sour cultures are chosen when acidity or unconventional fermentation character is an intentional part of the finished beer. Ale and Lager strains primarily provide predictable alcoholic fermentation, while Belgian strains emphasize expressive fruity esters and spicy phenols without necessarily making the beer sour. Sour cultures can behave very differently: some produce noticeable acidity quickly, while mixed cultures may continue developing for months or even years as different microorganisms become active. Beginning brewers should pay close attention to the manufacturer’s recommended temperature, fermentation method, and sanitation practices, while experienced brewers can use culture selection, aging time, oxygen exposure, hopping rates, and blending to shape acidity, attenuation, funk, and overall complexity.

***Cross-Contamination Warning***: Sour cultures may contain bacteria and wild yeast that can remain on brewing equipment and unintentionally affect future batches. To reduce the risk, consider keeping dedicated plastic and other difficult to sanitize equipment such as tubing, siphons, bottling equipment, and fermenter accessories specifically for sour beer production. Thoroughly clean and sanitize all equipment according to the sanitizer manufacturer’s instructions before and after use.