The birth mystery of lager beer may be solved as scientists discovered the yeast's genomic foundation that makes cold-brewing ale possible.

The parent yeast of lager is believed to have journeyed from Patagonia to Bavaria, giving birth to the most popular alcoholic beverage of today.

Researchers from Portugal, Argentina and the United States teamed up in the hunt for the yeast dubbed Saccharomyces eubayanus, whose genome was sequenced and confirmed as a near-perfect match as a parent of the lager yeast hybrid.

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 Chris Todd , a University of Wisconsin-Madison genetics professor and a co-author of the study in the Proceedings of the National Academy of Sciences.

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People have been hunting for this thing for decades, said Hittinger. 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.

They claim that, around 500 years ago, the microbe traveled 7,000 miles from South America to Bavaria, the home of lager beer.

According to Hittinger, the newfound yeast is prevalent in the beech forests of Patagonia, and have not been spotted elsewhere.

When eggs laid by insects on tree leaves stimulate sugar-rich bulbous materials called galls, the yeast strain is produced and spontaneously ferment, according to the scientists.

Those galls are very sugar-rich and ferment the tree. You can smell it in the forest, Hittinger said. Local people in this area would chop these galls off and eat them in salads.

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 Diego Libkind of the Institute for Biodiversity and Environment Research (CONICET) in Bariloche, Argentina.

While how the travel was achieved remains unknown, the researchers suggested that the yeast may have been carried on a sailing ship across the Atlantic ocean, in a piece of wood or the gut of a fruit fly.

Furthermore, its ability to endure cold weather would have allowed its entry into the lager-brewing chain.

As the Bavarians began the process of lagering in the 15th century, said Hittinger, they would brew and store their beer in caves or cellars and keep it at a constant cool temperature.

And that's how a new yeast was created, he suggested.

The findings were published in the journal Proceedings of the National Academy of Sciences on Monday.

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