The yeast needed to brew pale lagers and dark stouts alike has a long and complex pedigree that traces back to yeasts used for European and Asian wines.
Ales, such as the classic English bitters, are fermented by brewer’s yeast (Saccharomyces cerevisiae), while lagers are fermented by Saccharomyces pastorianus, a cross between brewer’s yeast and Saccharomyces eubayanus. To pinpoint the origins of beer yeast, Justin Fay at the University of Rochester in New York and his colleagues sequenced the genomes of 47 yeast strains.
The team found that beer-brewing strains derive their ancestry from close relatives of yeasts used in Europe to ferment wine grapes and from relatives of Asian strains that produce rice wine such as sake. But the researchers also found the genomic fingerprints of mysterious strains that are either unknown or extinct.
The geographic origin of grape-wine yeast is debated, but if it was domesticated in Europe, it might have interbred with Asian yeast along the Silk Road to give rise to beer yeast, the authors say.