Almost Every Loaf and Beer Comes from One Domesticated Microbe

Saccharomyces cerevisiae is one species. The cube of compressed yeast in a supermarket fridge, the cloudy yeast at the bottom of a Belgian saison, the smear of cells in a winery's lees — different strains, but the same organism, and one we've been carrying around for at least 5,000 years.

The migration story has only come into focus recently. Sequencing 651 strains from 56 countries, a 2018 study in Current Biology and follow-on work argued that cerevisiae originated in East Asia and moved west roughly 14,000 to 16,000 years ago, along the routes that would later become the Silk Road. The wild ancestor still lives in Chinese oak forests; everything in our kitchens descends from a few founder lineages that left.

Domestication produced four loose genetic clusters: bread, beer, wine, sake. Bread strains are usually tetraploid — they carry four copies of their genome, a kind of redundancy that helps them tolerate the punishing osmotic stress of sweet doughs. Beer strains lost the ability to make spores; they don't need to, fermenting in liquid year-round. Wine strains tolerate higher alcohol than the wild type. Each cluster is the fingerprint of a different human industry that selected for a different trait.

The first commercial bakers' yeast went on sale in the Netherlands in 1780, decades before anyone — including Pasteur — knew what yeast actually was. Sourdough is the holdout: most starters carry diploid wild strains the baker captured from the air, the flour, or their hands, which is why a starter from San Francisco genuinely tastes different from one in Bari.