Hardy perennial: Patagonian yeast Saccharomyces eubayanus thrives at colder temperatures – vital for lager manufacture Photograph: Diego Libkind

Lager drinkers can thank the birds for their favourite tipple. That is the conclusion of US scientists who say the yeast involved in making their beloved amber nectar could have been spread round the planet by migrating birds.

The work, by researchers at the University of Wisconsin-Madison, follows up on the 2011 discovery that a key component of the yeast used to make cold-brewed beers came from Patagonia, in South America.

Lager – which, say its multitudinous fans, has a crisper, cleaner taste than warm-brewed ales – was first made by monks in Bavaria 500 years ago, using a yeast that has since been shown to be a hybrid of European yeast and another yeast. It was this latter yeast that was traced to colonies found in trees in Patagonia three years ago.

The discovery raised a critical question, however. How did that yeast make it from South America to Europe, a 7,000-mile journey, and there form a hybrid with an old world version? When the discovery of the Patagonian link was announced, most speculation focused on the idea that the yeast could have arrived in the timbers of boats of early traders to and from South America.

But new research by Professor Chris Hittinger, at the University of Wisconsin-Madison, and published in Molecular Ecology, indicates that this scenario now looks unlikely. The timing does not fit, he says.

“We have found two distinct, well-established populations of the Patagonia yeast, Saccharomyces eubayanus,” says Hittinger. “Both have adapted to the cold there – and of course that is what makes their contribution to lager yeast so important. The yeasts live in trees, which seem to provide everything they need. They are happy there.”

But occasionally, the yeast sends out colonists, he adds. “What we think is happening is that well-established, genetically diverse populations are sending migrants round the world. Generally, they are not successful, but occasionally they are.”

One of these colonies has since been found in North America – at Sheboygan Indian Mound Park in Wisconsin – although the yeast exists there in very low concentrations. Hittinger also believes another colony of Saccharomyces eubayanus was established in Europe. “It may still exist today although we have tried very hard to find it without any success.”

Thus the Wisconsin researchers speculate that a colony of the Patagonia yeast became established in Europe or the Middle East, most probably several thousand years ago. “We do not know if it still survives. So far we have had no luck in our search,” adds Hittinger.

The crucial point is that yeast from this colony later must have hybridised with European yeast and that hybrid was picked up by monks who were making beer in caves and cellars in Bavaria. Their brews using the hybrid yeast ran at much lower temperatures and produced the crisper, lager-type beers for which the region has become famous – all thanks to an unexpected Patagonian import.

The question remains: how did the yeast arrive in Europe in the first place? “If I had to bet, I would lay money on migrating birds,” says Hittinger. “There are well established migrations routes for birds from Patagonia to North America and from there are routes that could take it to Europe after that.”

The crucial point is that it would only take a single cell of cold-adapted Saccharomyces eubayanus to survive the journey over the Atlantic. From this, it could have grown and established a colony in Europe and then later formed a hybrid in Germany. The end result was the chilled, amber liquid that is now the most widely made and widely sold type of beer in the world.