Thursday, August 25th, 2011 at 12:12 pm in On Beer.
Recently, a group of eight scientists posited a theory that a newly discovered yeast strain, dubbed Saccharomyces eubayanus, may have hitched a ride from Patagonia, in South America, to Europe where it got busy with local yeasts there — notably Saccharomyces cerevisiae — to form the yeast we know today as lager yeast, or Saccharomyces pastorianus (a.k.a. Saccharomyces carlsbergensis).
The academic paper, to be published in the August edition of the journal Proceedings of the National Academy of Sciences of the United States of America (or PNAS), goes by the rather dry title, Microbe domestication and the identification of the wild genetic stock of lager-brewing yeast. The Abstract summarizes the paper:
Domestication of plants and animals promoted humanity’s transition from nomadic to sedentary lifestyles, demographic expansion, and the emergence of civilizations. In contrast to the well-documented successes of crop and livestock breeding, processes of microbe domestication remain obscure, despite the importance of microbes to the production of food, beverages, and biofuels. Lager-beer, first brewed in the 15th century, employs an allotetraploid hybrid yeast, Saccharomyces pastorianus (syn. Saccharomyces carlsbergensis), a domesticated species created by the fusion of a Saccharomyces cerevisiae ale-yeast with an unknown cryotolerant Saccharomyces species. We report the isolation of that species and designate it Saccharomyces eubayanus sp. nov. because of its resemblance to Saccharomyces bayanus (a complex hybrid of S. eubayanus, Saccharomyces uvarum, and S. cerevisiae found only in the brewing environment). Individuals from populations of S. eubayanus and its sister species, S. uvarum, exist in apparent sympatry in Nothofagus (Southern beech) forests in Patagonia, but are isolated genetically through intrinsic postzygotic barriers, and ecologically through host-preference. The draft genome sequence of S. eubayanus is 99.5% identical to the non-S. cerevisiae portion of the S. pastorianus genome sequence and suggests specific changes in sugar and sulfite metabolism that were crucial for domestication in the lager-brewing environment. This study shows that combining microbial ecology with comparative genomics facilitates the discovery and preservation of wild genetic stocks of domesticated microbes to trace their history, identify genetic changes, and suggest paths to further industrial improvement.
Mainstream media, picking up the story, has sensationalized it, looking for the human angle. For example the L.A. Times compared the discovery to finding the evolutionary missing link, titling their piece Scientists find lager beer’s missing link — in Patagonia. Essentially, they detail the scientists’ five-year quest to answer the question of where lager yeast originated, and how it came to be. The answer, according to the new paper, is a newly found strain of yeast discovered in the forests of Argentina’s Patagonia region. The wild yeast was named Saccharomyces eubayanus, and it was found living on beech trees.
According to the Times’ report:
Their best bet is that centuries ago, S. eubayanus somehow found its way to Europe and hybridized with the domestic yeast used to brew ale, creating an organism that can ferment at the lower temperatures used to make lager.
Geneticists have known since the 1980s that the yeast brewers use to make lager, S. pastorianus, was a hybrid of two yeast species: S. cerevisiae — used to make ales, wine and bread — and some other, unidentified organism.
Then one of the eight, Diego Libkind, a professor at the Institute for Biodiversity and Environment Research in Bariloche, Argentina, discovered sugar-rich galls on southern beech trees in Patagonia. Yeast were drawn to the galls like a moth to a flame, and had been used by native populations to make a fermented beverage. The yeast in the galls was sent to the University of Colorado, who analyzed the genome, finding that it was 99.5% identical to lager yeast. They named the new yeast Saccharomyces eubayanus, presumably because of its similarity to Saccharomyces bayanus, a yeast commonly used to make cider and wine. Said Stanford geneticist Gavin Sherlock, quoted in the L.A. Times: “The DNA evidence is strong.”
Naturally, Sherlock, and many others have been wondering how Saccharomyces eubayanus hitched a ride to Bavaria at a time when there was no known contact between the two parts of the world, separated by an ocean and some 8,000 miles. The article also states that “Lager was invented in the 1400s,” though my memory is that European brewers were using lager yeast well before that, and it was the lagering process was developed in the 1400s, but perhaps I’m not remembering that correctly.
In an interesting development surrounding this debate, U. Penn biomolecular archeologist, Patrick McGovern (author of Uncorking the Past), weighed in with his thoughts at the MSNBC article about this story, Beer mystery solved! Yeast ID’d. Here’s what McGovern had to say, as summarized by author John Roach:
Assuming the genetics work is correct, he said he is “troubled by how this newly discovered wild yeast strain made it into Bavaria in the 1500s.”
For one, he noted, Germans, and especially Bavarians, were not involved in the European exploration of Patagonia at the time. So, if the yeast somehow hitched a ride back to Europe via trade with the English, Spanish, and Portuguese, how did it get to Bavaria?
“Perhaps, some Patagonian beech was used to make a wine barrel that was then transported to Bavaria and subsequently inoculated a batch of beer there?” he asked. “Seems unlikely.”
He said a more likely scenario is that galls in the oak forests of southern Germany also harbored S. eubayanus, at least until it was out competed by the more ubiquitous S. cerevisiae.
“If true, then the use of European oak in making beer barrels and especially processing vats, which could harbor the yeast, might better explain the Bavarian ‘discovery’ of lager in the 1500s,” he said.
Nevertheless, he added, history and archaeology are full of surprises.
“Nowhere is this more true than of the seemingly miraculous process of fermentation and the key role of alcohol in human culture and life itself on this planet,” he said.
“This article has begun to unravel the complicated heritage and life history of the fermentation yeasts, and will hopefully stimulate more research to see whether the Patagonian hypothesis proves correct.”
Diplomatically put, because as everyone admits, the find in South America may not be the exclusive area where Saccharomyces eubayanus lives, just the first place it’s been found. The human history portion of this story doesn’t seem to quite fit at this point, but it’s certainly a compelling story and it will be interesting to see how it continues to develop.