Which yeast species is commonly used in lager beer fermentation?

Which yeast species is commonly used in lager beer fermentation? Saccharomyces pastorianus is the standard answer.

Lager brewing is associated with cool fermentation and extended cold conditioning, or “lagering.” S. pastorianus is commonly called a bottom-fermenting yeast because many strains settle toward the bottom of the fermenter, although that behavior is not an absolute rule.

The species has an unusual history: its genome is a hybrid assembled from Saccharomyces cerevisiae and Saccharomyces eubayanus. That combination helps lager strains tolerate cold temperatures while fermenting important malt sugars. The older name S. carlsbergensis still appears in historical and scientific writing, but S. pastorianus has priority as the accepted name.

Lager yeast should not be confused with S. cerevisiae, the species most associated with ale fermentation. The distinction is useful, but brewing practices overlap: temperature, strain selection, conditioning, and recipe all influence the finished beer.