Researchers find an elusive European parent of lager yeast in Ireland

A new paper in FEMS Yeast Research reports that, for the first time in Europe, scientists have discovered the ancestor of the yeast species necessary for the production of lager beer.

Brewing is one of the oldest human industries. Scientists have uncovered evidence of fermented beverages from China from at least 7,000 years ago, and from Israel from up to 13,000 years ago. Modern brewing developed in Europe, where until the Middle Ages, most beer brewing was associated with a yeast called Saccharomyces cerevisiae. This is the same species of yeast that is still used today to make ale-style beer, wine, and bread.

Most beer made nowadays, however, is lager beer, not ale, and there is considerable interest in understanding the historical shift from ale to lager in Europe. Lager brewing, which first appeared in the 13th century in Bavaria, uses a different species of yeast, Saccharomyces pastorianus.

S. pastorianus is a hybrid of two parents, only one of which is S. cerevisiae. The identity of the second parent was a mystery until 2011, when Saccharomyces eubayanus was discovered in the Patagonian Andes in South America. Like S. pastorianus, S. eubayanus is cold-tolerant, and scientists believe that the lager-style of cold brewing was selected for the formation of the S. pastorianus hybrid yeast from an ale strain of S. cerevisiae and a wild S. eubayanus isolate.

Although the records show that the first use of S. pastorianus was in breweries in southern Germany, the S. eubayanus parent was never found in Europe. Instead, researchers have discovered the yeast in South America, North America, China, Tibet, and New Zealand. This curiosity caused some researchers to wonder whether S. eubayanus had, in fact, ever been in Europe, and if not, from where the lager yeast S. pastorianus had come. But most recently, researchers at University College Dublin have discovered and isolated S. eubayanus in a wooded area of their campus.

The Irish researchers isolated two different S. eubayanus strains, from soil samples collected on the Belfield campus of University College Dublin, as part of undergraduate research projects to identify wild yeasts and sequence their genomes. The isolates came from soil on two sites on the university campus, about 17 meters apart, collected in September 2021. The genome sequences of these two isolates showed that they are related to the ancestral S. eubayanus strain that initially mated with S. cerevisiae to form S. pastorianus.

The discovery of S. eubayanus in Ireland shows that this yeast is native to Europe and it seems likely that it has lived in other parts of the continent. This new study supports the view that there were natural populations of the yeast in southern Germany in the Middle Ages and these provided the parents of the first lager yeast. The question of whether these ancient populations still remain hidden somewhere in the forests of Bavaria remains to be answered.

"This discovery is a fantastic example of research-led teaching," said the paper's lead author, Geraldine Butler. "Our undergraduates have found more than a hundred yeast species in Irish soil samples over the past five years, and we're delighted to stumble across S. eubayanus on our own doorstep. We're hoping to find a commercial partner to brew with it so we can find out what it tastes like."