Sunday, October 18, 2015

Did a parent of lager yeast originate in Tibet?

Research was published in 2011 which suggested that Saccharomyces eubayanus —one-half of lager yeast's parents— had originated in Patagonia (at the southern tip of South America). Scientists found it there, growing on the sides of native beech trees. Left unanswered was how the yeast would have traveled to Bavaria before Europeans began traveling to the Americas.

Research in 2014 may have provided an answer: maybe the initial cross-hybridization came earlier, not from South America, but from Asia. Researchers have discovered S. eubayanus yeast on the Tibetan Plateau showing a closer genetic match to modern lager yeast than that in the Patagonian forests.

From Lars Marius Garshol, a Norwegian beer author and blogger:
The two species that gave birth to lager yeast are S. cerevisiae and S. eubayanus, which is one of the cold-tolerant species. It has been known for decades that lager yeast was a hybrid of ale yeast and some other species, but which species was not known. Then S. eubayanus was discovered in 2011 in Patagonia, and was found to match 99.56% of the non-ale yeast part of the lager yeast genome. Initially there was some confusion as to how it managed to travel from Patagonia to Bavaria to work in lager brewing, when lager brewing began before any European visited Patagonia.

However, in 2014 S. eubayanus was found on the Tibetan plateau in Tibet and the western Chinese provinces of Qinghai, Sichuan and Shaanxi. The yeasts found here turned out to match the S. pastorianus genome even more closely, so it seems likely that the ancestors of lager yeast came from this area. Given that the Silk Road passed through this area that provides an possible explanation for how the yeast came to Europe. When the hybrid was formed, and where, remains unknown.

Very likely, what happened was that the early lager brewers were brewing with mixed yeast cultures. That's what kveik is, and these yeast cultures will have been treated the same way. Probably the brewers began by fermenting at relatively, but not very, cold temperatures. This will have given cold-tolerant yeasts an advantage. At some point, already-formed S. pastorianus got into the fermentation, or it was formed in a brewery. At that point, evolutionary pressure towards tolerating cold would have caused it to out-compete the other yeasts, and lager brewing with S. pastorianus began.

krausen for priming

Interestingly, S. pastorianus is divided into two groups, which may have arisen separately. One is the Saaz group, which was used in the Czech Republic and by Carlsberg. The other is the Frohberg group, which was used by other Danish breweries and also in the Netherlands. (What did the areas not mentioned here use? The literature doesn't say.) Frohberg has lost most of the S. eubayanus r-DNA, while Saaz has lost most of the ale yeast genome, so these two groups are quite different. Saaz seems to produce less higher alcohols and esters during fermentation, which is also interesting.

Read the rest of the story at LarsBlog: The Saccharomyces family, part of Mr. Garshol's informative three-part series on yeast.

  • The Patagonian research was a cooperative study between the University of Wisconsin-Madison and the Institute for Biodiversity and Environment Research in Bariloche, Argentina, published in 2011 in the Proceedings of the National Academies of Sciences.
  • The Tibetan research was conducted by State Key Laboratory of Mycology at the Chinese Academy of Sciences, and published in 2014.

  • For more from YFGF:

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