The mystery behind the birth of lager beer has gained a new clue through the discovery of elusive species of wild yeast in the frozen forests of Patagonia in Argentina.

Taking a 7,000-mile journey around 500 years ago, the parent yeast of lager beer is now believed to have traveled from Patagonia to Bavaria, possibly on a sailing ship.

Researchers from Portugal, Argentina and the United States teamed up in the hunt for the yeast, which was named as Saccharomyces eubayanus.

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.

Yeasts, which are microscopic fungi living off sugar, can concert it to carbon dioxide and alcohol through fermentation, leading up to creating beer.  

Since the 1980s, scientists have known that yeast is used in lager production, was a hybrid of two yeast species. Only one player, S. cerevisiae, was identified, while the other organism remained a puzzle. Scientists were unable to find this missing link among the 1,000 or so species of yeast known to science.

The hybrid yeast could survive because brewers preserve some of the lager each time to seed the next batch with the same yeast.

The hybrid almost definitely formed accidentally and people adopted it because the beer came out differently, said Chris Hittinger, evolutionary biologist from the University of Wisconsin in Madison, who was a part of the research team.

This year, researchers have identified the wild yeast that, in the age of sail, apparently traveled more than 7,000 miles to those Bavarian caves to make a fortuitous microbial match that today underpins the $250 billion-a-year lager beer industry.

The genome of the newfound yeast was sequenced and revealed 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.

According to Hittinger, the newfound yeast is prevalent in the beech forests of Patagonia, and have not been spotted elsewhere. The forests, with daily lows of around 28 ºF, make perfect seedbed for the lager-brewing yeast.  

When eggs laid by insects on tree leaves stimulate sugar-rich bulbous materials called galls, the yeast strain is produced andspontaneously 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.

Scientists still were unable to find how yeast traveled from South America to the caves and monasteries of Bavaria where lager beer was born. But lager beer brewing began at about the same time as the rise of trans-Atlantic trade, so the yeast may have hitched a ride on a sailing ship, perhaps on a piece of wood or in the stomach of a fruit fly.     

As the Bavarians began the process of laagering 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, creating a new yeast. 

That cold-loving hybrid then evolved into the modern lager yeasts that are used today in breweries throughout the world, acquiring several genetic changes that altered their sugar and sulfur metabolism.  

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