With beer there is a choice for drinkers: ales and lagers. The difference between these two beverages comes down to the type of yeast used. In the brewing world there are ale yeasts (diverse in number) and lager yeasts (a narrower stream.) Importantly, the type of yeast used affects the temperature at which the beer is fermented, with ales made at warmer temperatures.
The original yeast used for brewing — Saccharromyces cerevisiae — is also commonly used to make wine and bread. This yeast is still the basis of most ales (and what are now popularly termed ‘craft beers.’) With lager, different yeast is used. This was stumbled on by accident when Bavarians, in the fifteenth century, noticed that beer stored in a beer store (a “lagern”) continued to ferment. The end product was a smoother beer. This beer came to be called lager or lager beer (and often just beer.) This type of beer is the dominant brew today, with 90 percent of the world market.
The yeast used in larger is a hybrid, formed between the yeasts S. cerevisiae and S. eubayanus. A new study has deconstructed the genome of S. eubayanus to work out its origins. To do this, the research group also studied a wild yeast, of the same species, from Patagonia. Patagonia is a sparsely populated region located at the southern end of South America, shared by Argentina and Chile.
The findings show that the process leading to the lager yeast was not a smooth one and that gene sharing took place between different strains of S. eubayanus and with S. cerevisiae to produce the current hybrid yeast. At least two major gene sharing events are thought to have occurred over the history of the yeast. This is particular so with the energy powerhouse of the yeast, what is termed the mitochondrial genome sequences.
One of these events has arisen through ‘domestication’ through brewing. Here the genes for fermentation and sugar metabolism are quite distinct in the strain used for brewing compared with the Patagonian isolate. This means that the yeast has moved from an organism that consumes alcohol to one that produce sit. This pattern was shown across two distinct lineages of the yeast, termed Saaz and Frohberg lineages, after their area of origin.
The research has been published in the journal Molecular Biology and Evolution. The research is titled “The genome sequence of Saccharomyces eubayanus and the domestication of lager-brewing yeasts.”