The study has been conducted to determine that monks from the 15th century made use of a foreign yeast strain for making lager beer.
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While the earliest yeasts known to man have been used for millennia to make ales, bread and wine, lager beer – and the yeast used to create it – dates to just 500 years ago. But no one was sure what other yeast strain had mixed with the ale yeast to make the lager hybrid. The second kind of beer, however, is a 15 century innovation discovered first by the Bavarians who noticed that beer kept in caves over winter would continue to ferment.
Thus, a smoother and lighter beer began dominating 19 and 20 century among beer enthusiasts, especially in America.
To explore the evolutionary origin of lager yeast, Hittinger, doctoral candidate EmilyClare Baker and former student Bing Wing used advanced genome sequencing and informatics techniques to trace the two major strains of lager yeast to a combination of two pre-existing yeasts: S. cerevisiae and S. eubayanus.
Taking advantage of a newly described wild yeast species from Pata gonia, Saccharomyces eubayanus, University of Wisconsin-Madison researchers were able to complete and assemble a high-quality genome of S eubayanus using next-generation sequencing.
“There’s going to be a lot of opportunities”, said Chris Hittinger, of the University of Wisconsin-Madison, in an interview with Laboratory Equipment. The researchers have made its comparison to domesticated hybrids that have been used for brewing lager and that has allowed the ability of studying the entire genomes of both the parental yeast species that have contributed to lager beer for the first time ever. The correlation between the two species of yeast – S. cervisiae and S. eubayanus – as different as humans and birds, happened twice, at the least.
Not until recently, lagers were thought to contain a single species of yeast called the Saccharomyces pastorianus syn.
Yeast sexually reproduces, forming unique strains, only when the cells are stressed, the researchers said. The Saaz and Frohberg lineages (named for their region of origin), were both born from almost identical strains of S. eubayanus and diverse ale strains of S. cerevisiae. Typically, lagers utilize yeasts that could ferment at lower temperatures, a process that gives them their distinctively crisp taste.
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He added that in spite of their differences, these hybrids benefitted from domestication over time, which modified them in predictable ways until they became what they are today. When compared to the pure S.eubayanus, today’s lager yeast has indeed evolved significantly in specific sets of genes, specifically those involved in fermentation and sugar metabolism.
