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.

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.

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Pic(k) of the Week: High Kräusen

At Oliver Breweries at the Pratt Street Alehouse, in downtown Baltimore, Maryland, the beer is fermented in open vats. Viable yeast is skimmed from the uppermost, spumous, layer of the fermenting beer —called kräusen (pronounced KROY [like boy] zen) —and used to ferment the next batch of beer.

Here, the fermentation, although still quite active, has already passed the most active stage of fermentation called high kräusen. Notice the yeast and protein crust on the side walls of the fermenter, above the active yeast layer.

Open fermentation is traditional method of fermentation, unlike the current practice of almost all breweries in the U.S. —and worldwide— of fermenting beers in closed vessels, and collecting the yeast after fermentation in cone-shaped sections at the bottom of the fermenters.

Oliver Ales
Baltimore, Maryland.
11 February 2011.

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• Pic(k) of the Week: one in a weekly series of personal photos, often posted on Saturdays, and often, but not always, with a good fermentable as a subject.
• Commercial reproduction requires explicit permission, as per Creative Commons. For non-commercial purposes, no permission is required (but kindly link back).
• Caveat lector: As a representative for Select Wines, Inc. —a wine and beer wholesaler in northern Virginia— I sell the beers of Oliver Ales.

Flocculating in public

Flocculation is one of those evolutionary traits of yeast that —Godisgood*— is essential to creating beer.

As any brewer will tell you, the yeast used to make beer tends to bunch up during fermentation. However, despite thousands of years of brewing and decades of genetic research on yeast, no one was able to explain why yeast stuck together.

But now, scientists at Harvard University have at last identified the specific gene that enables yeast to, ahem, flocculate.

That gene allows the normally solitary yeast cells to shield themselves from toxins in their environment by banding together in protective balls. Since one of those toxins is the ethanol that the yeast themselves produce, grouping together allows the yeast to survive in the alcohol-rich environment that results from brewing [emphasis mine].

More from Beer Brings Yeast Together, by Stuart Fox, posted 11.20.2008 at PopSci.com:

The gene, called FLO1, produces a Velcro-like protein on the outside of the yeast cells. When a yeast cell bumps into another cell with the same gene, they stick together. <...>

Over time, the yeast cells with FLO1 weed out the freeloaders, pushing them to the outside of the ball. Through this process, the freeloading cells not only don't get the benefit of being in the yeast ball, but they pay a cost by acting as the first line of defense for the yeast flock.

It's almost like game theory for yeast.

And, for Kevin Verstrepen, the lead scientist of the Harvard study, "who got his biology PhD from the Center for Malting and Brewing at the University of Belgium"

this is just one more example of how much the science of beer has to offer the science of biology.

Extrapolating from unicellular biology to group sociology, sometimes it is all about the beer.

• * Godisgood: a term once used by brewers to describe the beneficent activity of yeast without understanding its nature. Or maybe they did.
• Alerted to this story by Alan McLeod at A Good Beer Blog.