Lager is a bottom-fermented beer, meaning that the yeast settles at the bottom of the fermentation vessel. This is in contrast to top-fermented ales, where the yeast rises to the top. Lagering, the process of cold-conditioning the beer after fermentation, gives lagers their characteristic crisp, clean flavour.
The researchers, from the Technical University of Munich, analysed the DNA of yeast strains from a variety of historical and modern lager beers. They found that modern lager yeasts are all descended from a single strain of yeast that originated in Bavaria in the 16th century.
This strain of yeast, known as Saccharomyces pastorianus, is a hybrid of two other yeast species, S. cerevisiae and S. eubayanus. S. cerevisiae is the yeast used to make ale, while S. eubayanus is a cold-tolerant yeast found in the Patagonian region of South America.
The researchers believe that S. pastorianus originated when these two yeasts accidentally hybridised in a brewery in Bavaria. The new hybrid yeast was able to ferment beer at lower temperatures than either of its parent strains, and this allowed brewers to produce a more consistent and flavorful beer.
The discovery of the origins of lager yeast sheds light on the history of brewing in Bavaria and the development of one of the world's most popular beers.
