Secret of lager beer yeast discovered

MADISON, Wis., Aug. 23 (UPI) -- U.S. scientists say the birthplace of a yeast strain that gave the world lager beer almost 500 years ago has been discovered.

A possible stowaway from the New World, the yeast is believed to have fused with a distant relative 500 years ago in the cool caves and monastery cellars where European brewers stored their product, and gave us lager. The clear, cold-fermented beer first brewed by 15th century Bavarians is arguably the most popular alcoholic beverage in the world.

Scientists have long known the yeast that gives beer the capacity to ferment at cold temperatures was a hybrid, but only Saccharomyces cerevisiae -- the yeast that had always been used to leaven bread and ferment wine and ale -- was known. Its partner, which conferred on beer the ability to ferment in the cold, remained elusive as researchers were unable to find it among the 1,000 or so species of yeast known to science.

Now researchers say they believe they have identified a wild yeast that, in the age of sail, apparently traveled more than 7,000 miles from the beech forests of Patagonia, the alpine region at the tip of South America, to those Bavarian caves.

"People have been hunting for this thing for decades," study co-author Chris Todd Hittinger, a University of Wisconsin-Madison genetics professor, said in a UWM release Monday. "And now we've found it. It is clearly the missing species. The only thing we can't say is if it also exists elsewhere (in the wild) and hasn't been found."

The yeast, dubbed Saccharomyces eubayanus, was discovered in galls that infect beech trees.

"Beech galls are very rich in simple sugars. It's a sugar-rich habitat that yeast seem to love," Hittinger says.

Researchers quickly sequenced the yeast's 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," Hittinger said.