lagering

Lagering is the stage of beer production in which beer is aged and conditioned at cold temperatures after primary fermentation. The term comes from the German lagern, meaning to store or keep, reflecting its historical use in storing beer for maturation. Lager beers rely on a bottom-fermenting yeast, typically Saccharomyces pastorianus, which ferments best at cooler temperatures than ale yeasts.

After primary fermentation, which generally occurs around 7–13 C, the beer is transferred to a cold conditioning or lagering vessel. The temperature during lagering is often near or below 0–4 C, and the duration ranges from several weeks to several months depending on the style and beer gravity. During this time, unwanted compounds such as diacetyl are reabsorbed by yeast, conditioning agents settle, proteins drop out, and hop and malt flavors mellow.

Lagering improves clarity and shelf stability; it also yields a crisper, smoother mouthfeel with reduced esters and phenolics relative to many ales. The process can involve a diacetyl rest before cold conditioning to help eliminate buttery notes, as well as careful temperature control and pressure management for carbonation.

Many traditional lager styles, including pilsner, helles, Dortmunder, and Märzen, rely on lagering to achieve their characteristic profile. Modern breweries also use cold conditioning to mature beers labeled as lagers, sometimes extending the process for higher-gravity beers or for premium products. Lagering remains a defining step in producing many widely consumed pale and amber beers.