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, and scientists have uncovered evidence of fermented beverages from China at least 7,000 years ago and Israel as far back as 13,000 years ago.
Modern brewing developed in Europe, where, until the Middle Ages, most beer production was associated with a yeast called Saccharomyces cerevisiae.
Today this yeast species is still used to make ale-style beer, wine, and bread.
However, most of the beer brewed today is lager, not ale, and there is much interest in understanding the historical transition from one to the other.
Lagers are fermented using a top-fermenting yeast at cool temperatures, while ales are fermented with a top-fermenting yeast at much warmer temperatures.
Lager, which first appeared in Bavaria in the 13th century, uses a different species of yeast, Saccharomyces pastorianus.
This is a hybrid of two parents, only one of which is S. cerevisiae.
Until 2011, the identity of the second parent was a mystery, when Saccharomyces eubayanus was discovered in the Patagonian Andes of South America.
Like S. pastorianus, S. eubayanus is cold tolerant.
While records show that the earliest use of S. pastorianus was in southern German breweries, the parent S. eubayanus has never been found in Europe.
Instead, researchers have discovered yeast in South America, North America, China, Tibet and New Zealand.
This has led some researchers to question whether S. eubayanus had ever been to Europe and, if not, where the lager yeast S. pastorianus came from.
But now researchers at University College Dublin have discovered and isolated S. eubayanus in a wooded area of their campus.
The researchers isolated two different strains of S. eubayanus from soil samples collected on the Belfield campus of University College Dublin as part of university research projects to identify wild yeasts and sequence their genomes.
The samples come from the soil of two university campus sites, approximately 17 meters apart, collected in September 2021.
According to the study, the genome sequences of these two isolates showed that they are related to the ancestral strain of S. eubayanus which initially mated with S. cerevisiae to form S. pastorianus.
The researchers say the discovery of S. eubayanus in Ireland demonstrates that this yeast originated in Europe and seems likely to have lived in other parts of the continent.
This new study supports the idea that natural yeast populations existed in southern Germany in the Middle Ages and that these provided the parents of the first lager yeast.
Lead author of the paper, Geraldine Butler, from University College Dublin, said: ‘This discovery is a fantastic example of research-led teaching.
“Over the past five years our students have found more than 100 species of yeast in Irish soil samples and we are delighted to come across S. eubayanus on our doorstep.
“We’re hoping to find a business partner to brew the beer with so we can find out what it tastes like.”
The research is published in FEMS Yeast Research.