London : Using novel sequencing techniques, a team of US researchers have traced the origins of the yeast used in making most popular lager beer all the way back to 15th century Bavaria in southeastern Germany. The team from University of Wisconsin-Madison found that the lager beer was created during the 15th century when Bavarians first noticed that beer stored in the caves during the winter continued to ferment. The result was a lighter and smoother beer that, after sharing it with their neighbouring Bohemians, went on to dominate 19th and 20th century beers tastes, especially in America. The beer world is divided into ales and lagers. The original and highly versatile yeast, Saccharromyces cerevisiae, has been used for millennium to make ales, wine and bread.While lagers now represent 94 percent of the world beer market, the origins of different hybrid lineages has been a bone of contention for lager beer makers. In 2011 it was discovered that lager yeasts are hybrid strains, made of two different yeast species - S. cerevisiae and S. eubayanus. Researchers have now found there were two “origin events” for them. “Lager yeasts did not just originate once. This unlikely marriage between two species, genetically as different from one another as humans and birds, happened at least twice,” said Chris Todd Hittinger from University of Wisconsin-Madison. “Although these hybrids were different from the start, they also changed in some predictable ways during their domestication,” he noted. Taking advantage of a newly described wild yeast species from Patagonia, Saccharomyces eubayanus, the research team was able to complete and assemble a high-quality genome of S. eubayanus using next-generation sequencing. They compared it to domesticated hybrids that are used to brew lager style beers, allowing for the first time the ability of study the complete genomes of both parental yeast species contributing to lager beer. They show two independent origin events for S. cerevisiae and S. eubanyus hybrids that brew lager beers. The results suggest the Saaz and Frohberg lineages - named after their area of origin in Bavaria - were created by at least two distinct hybridisation events. The findings, published in the journal Molecular Biology and Evolution, have now clarified the origins of the major lineages of the hybrid yeasts used to brew lagers. “It will provide a roadmap for future research in the domestication of lager yeasts,” the authors concluded.