For the first time in Europe, scientists have discovered the ancestor of the yeast species needed to produce lager beer.
Brewing is one of the oldest human industries, and scientists have discovered evidence of fermented beverages from China at least 7,000 years ago and from Israel 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.
Today, this species of yeast is still used to make beer, wine, and ale-style bread.
However, most beer made today is lager, not ale, and understanding the historical shift from one to the other is very interesting.
Lagers are fermented using bottom-fermenting yeast at cool temperatures, while ales are fermented with top-fermenting yeast at a much warmer temperature.
The brewing of lager beer, which first appeared in the 13th century in Bavaria, uses another species of yeast, Saccharomyces pastorianus.
It 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 in South America.
Like S. pastorianus, S. eubayanus is cold tolerant.
While records show that the first use of S. pastorianus was in breweries in southern Germany, the parent S. eubayanus has never been found in Europe.
Instead, researchers have discovered the yeast in South America, North America, China, Tibet and New Zealand.
This has led some researchers to question whether S. eubayanus was in fact ever found in Europe, and if not, where the lager yeast S. pastorianus came from.
But now researchers from University College Dublin have discovered and isolated S. eubayanus in a wooded area on their campus.
Researchers isolated two different strains of S. eubayanus from soil samples taken from the Belfield campus of University College Dublin, as part of undergraduate research projects aimed at identifying wild yeasts and sequencing their genomes.
The samples are from soils at two sites on the university campus, 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 that initially mated with S. cerevisiae to form S. pastorianus.
The researchers say the discovery of S. eubayanus in Ireland shows that this yeast originated in Europe and it seems likely that it lived in other parts of the continent.
This new study supports the idea that there were natural populations of the yeast in southern Germany in the Middle Ages and that these provided the parents of the first lager yeast.
The paper’s lead author, Geraldine Butler, of University College Dublin, said: “This discovery is a fantastic example of research-based teaching.
“Our undergraduate students have found over a hundred yeast species in Irish soil samples over the past five years, and we are delighted to come across S. eubayanus on our doorstep.
“We’re hoping to find a business partner to brew with so we can find out what it looks like.”
The research is published in FEMS Yeast Research.