The find sheds light on how early batches of lager were brewed.
People have been searching for the wild ancestor of lager yeast for decades.
Scientists finally located the yeast in the forest of the Patagonia region.
The find reveals how the first batches of European lager were brewed in cool caves of Bavaria.
Deep in the forests of South America's Patagonia region, scientists have tracked down the wild ancestor of the yeast that makes cold-brewing ale possible, according to a new study.
The finding provides the missing piece in a centuries-long tale of beer-drinking, today a $250 billion a year industry, that began with the first batches of European lager brewed in the cool, dank caves of Bavaria.
"People have been hunting for this thing for decades," said Chris Todd Hittinger, a University of Wisconsin-Madison genetics professor and a co-author of the study in the Proceedings of the National Academy of Sciences.
"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."
Researchers from Portugal, Argentina and the United States teamed up in the hunt for the yeast, now dubbed Saccharomyces eubayanus.
The origin of the the hybrid yeast used for making the popular golden brew has been a persistent mystery.
One element -- Saccharomyces cerevisiae, responsible for the warmer temperature fermentation of ale, wine and bread -- was well known.
But the other was a puzzle. Scientists at the New University of Lisbon, who pored over 1,000 species of known yeast in European collections in an attempt to find a match, but turned up nothing.
They expanded the search to international collaborators, and Diego Libkind of the Institute for Biodiversity and Environment Research (CONICET) in Bariloche, Argentina found a close match for the yeast in Patagonian beech trees.
The yeast seemed to thrive and spontaneously ferment in the sugar-rich bulbous formations called galls which arise when insects lay eggs on the tree's leaves.
"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," said Libkind.
Researchers at the University of Colorado School of Medicine sequenced the genome of the Patagonian yeast and found it was a near-perfect match to the element used to brew lager.perfect
"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," said Hittinger.
Researchers believe the forest yeast made its way to Bavaria's brewing caves as a stowaway when trade first began across the Atlantic Ocean, perhaps in a piece of wood or in the belly of a fruit fly.