Geneticists have discovered the wild yeast that is believed made possible cold-temperature fermentation -- and the creation of the first lager beers.
Writing in the [<span
class="Apple-style-span">Proceedings of the National Academy of Sciences](https://www.pnas.org/content/early/2011/08/17/1105430108), researchers from Portugal, Argentina and the USA, have announced the discovery of a yeast, which they claim travelled across the Atlantic in, possibly, the belly of a fruit fly or on a piece of wood, to fuse with a distant relative, the domestic yeast that was in common usage to make leavened bread and ferment wine and ale.
They write: "The resulting hybrid -- representing a marriage of species as evolutionarily separated as humans and chickens -- would give us lager, the clear, cold-fermented beer first brewed by 15th century Bavarians."
The common yeast is Saccharomyces cerevisiae but it is its fusion with the newfound yeast, dubbed Saccharomyces eubayanus that gave beer the capacity to ferment at cold temperatures.
The search began in Europe with the New University of Lisbon's José Paulo Sampaio and Paula Gonçalves. They sorted through European yeast collections and gathered new yeasts from European environments, but to no avail. The search was then widened and it was collaborator Diego Libkind of the Institute for Biodiversity and Environment Research (CONICET) in Bariloche, Argentina, who discovered a potential match in galls that infect beech trees.
Chris Todd Hittinger, a University of Wisconsin-Madison genetics professor and a co-author of the new study, says: "Beech galls are very rich in simple sugars. It's a sugar rich habitat that yeast seem to love." Libkind adds: "When overmature, they fall all together to the (forest) floor where they often form a thick carpet that has an intense ethanol odor, most probably due to the hard work of our new Saccharomyces eubayanus."
The yeast was sent to the University of Colorado School of Medicine, where a team that included Hittinger, Jim Dover and Mark Johnston sequenced its genome. "It proved to be distinct from every known wild species of yeast, but was 99.5 percent identical to the non-ale yeast portion of the lager genome," says Hittinger. The study revealed that the hybrid has mutated over time. "Our discovery suggests that hybridization instantaneously formed an imperfect 'proto-lager' yeast that was more cold-tolerant than ale yeast and ideal for the cool Bavarian lagering process," Hittinger adds. "After adding some new variation for brewers to exploit, its sugar metabolism probably became more like ale yeast and better at producing beer."
The team is now continuing its search to see if the newly found wild yeast exists in the wild anywhere else in the world.
This article was originally published by WIRED UK
