The strain of brewers’ yeast used to make beer, Saccharomyces cerevisiae, derives from versions used over thousands of years to make grape-wine in Europe and rice-wine in Asia, a new genetic analysis shows.
The analysis, which involved sequencing the genomes of 47 strains of brewers’ (or bakers’) yeast and 65 other strains of the same species, is published in the journal PLOS Biology.
Conducted by a team led by Justin Fay of the University of Rochester, US, the results reveal that beer-making S. cerevisiae is a very special fungus, indeed. In addition to being, as the researchers say, “the product of a historical melting pot of fermentation technology”, it also contains genes derived from a mysterious, unknown and possibly extinct, additional strain, and overall bears very little resemblance to any surviving wild strain.
The research goes some way towards clarifying the origins of brewers’ yeast – a species suborned into the service of humanity thousands of years before the discovery microbes or genetic signatures.
Brewers, too, being throughout history people obsessed with producing ever-better beers (or wines, or sakes) have long, knowingly or not, mixed yeast strains together in the search for the perfect drink. Indeed, the yeast used to produce lager, as distinct from ale, is a hybrid, combining S. cerevisiae with a second species, S. eubayanus (which itself has close genetic matches to wild populations found in Tibet and North America).
Modern brewers’ yeast, Fay and colleagues suggest, was the product of a long-distant intermingling of various strains that took place somewhere along the Silk Road.
The end result, though, much like the damp contents of a pub carpet at the end of a Friday night, is a substance with ingredients that cannot be precisely identified.
Strains of S. cerevisiae used in wine-making, the researchers note, “show a clear signature” of ancestral strains, and in turn provide the identifiable genetic basis for versions used in medical and pharmaceutical applications.
“Ale strains,” they point out, “with the exception of a few found related to sake and European wine lineages, have no obvious wild population from which they were derived.”
Instead, they note, ale yeast has arisen from the admixture of European and Asian wine strains – making it, perhaps, the first truly anthropogenic fungus in history.
The finding, the researchers conclude, “suggests that early industrial strains spread with brewing technology to give rise to modern beer strains, similar to the spread of domesticated plant species with agriculture”.
Andrew Masterson is a former editor of Cosmos.
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