Sláinte!
In 1516, the duchy of Bavaria in Germany imposed a law on its beer brewers meant to reserve ingredients like wheat and rye for the baking of bread.
The decree restricted brewers to using only barley, hops, water and yeast to make their libations, and set the prices for beer depending on the time of year. The law inadvertently limited brewing to the winter, which favored a cold-tolerant yeast called
Saccharomyces pastorianus, which brews lager, over the more common
S. cerevisiae, which brews ale
.
S. pastorianus is a hybrid, produced from the mating of
S. cerevisiae with another yeast called
S. eubayanus. Despite lager’s European origins,
S. eubayanus hadn’t actually been found there and was only first discovered in 2011,
in the Patagonia region of South America (
SN: 8/23/11).
Now, thanks to a research project carried out by undergraduate students, S. eubayanus has been found living in European soil — fittingly, in the beer-loving nation of Ireland.
“Since the discovery of
S. eubayanus [more than] 10 years ago, it’s been a fun puzzle putting together where the species is actually found,” says Quinn Langdon, a biologist at Stanford University, who was not involved with the study.
A leading theory is that
S. eubayanus originated in Patagonia and then spread around the world, eventually mating with
S. cerevisiae in European breweries to make
S. pastorianus.
Geraldine Butler, a geneticist at University College Dublin and leader of the project, always thought that teaching genome-sequencing techniques by having students scour soils for yeast could turn up
S. eubayanus. Still, she says, she couldn’t contain her excitement when she saw the first hint of the microbe. “I was sitting by the sequencer waiting for the results to come out,” she says.
One of Butler’s students, Stephen Allen, found two local strains of
S. eubayanus hiding in plain sight on the Belfield campus of University College Dublin. The team has since gone back and found the yeast again, Butler says, suggesting that there is a stable population of the yeast living in the Irish soil. ...
https://www.sciencenews.org/article/brewing-yeast-ancestor-ireland-beer