The mystery behind the birth of lager beer has been solved. Scientists have successfully traced the origin of the popular alcoholic beverage to a type of yeast, believed to have travelled 7,000 miles from Patagonia to Bavaria 500 years ago.

A team of researchers from countries including Portugal, Argentina and the United States say that after a five-year search around the world, they have discovered the genomic foundation of the yeast, dubbed as Saccharomyces eubayanus. The yeast's genome was sequenced and confirmed as a near-perfect match of the lager yeast hybrid.

Scientists are not yet sure how the elusive species of yeast managed to travel such a long distance. It may have been carried on a sailing ship across the Atlantic in a piece of wood or the gut of a fruit fly.

The possible man-aided migration from South America to Europe is indeed uncommon, but not unique,  Jose Paula Sampaio, a leader of the study from the New University of Lisbon in Portugal, told ABC.

Chris Todd Hittinger, a University of Wisconsin-Madison genetics professor and co-author of the study, said people have been hunting for it for decades.

It is clearly the missing species, said Hittinger. The only thing we can't say is if it also exists elsewhere and hasn't been found.

Hittinger added that the newfound yeast, which is prevalent in the beech forests of Patagonia and distinct from every known wild species of yeast, was 99.5 percent identical to the non-ale yeast portion of the lager genome.

Scientists said eggs laid by insects on tree leaves give rise to sugar-rich bulbous materials called galls in which the yeast strain flourishes and ferments spontaneously.

The sugar-rich galls ferment the tree and after getting overmatured, 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 Saccharomyces eubayanus, said Diego Libkind of the Institute for Biodiversity and Environment Research in Bariloche, Argentina.

Scientists also believe the yeast's ability to endure cold weather would have also allowed its entry into the lager-brewing chain.

It was in the 15th century that Bavarians began the process of lagering beer. They used to brew and store their beer in caves or cellars and keep it at a constant cool temperature. That's how the new yeast was created, Hittinger suggested.

To see what changes had occurred over the years, researchers compared the DNA of the wild Patagonian yeast with the DNA of lager yeast used in breweries and found that there were changes in genes that control sugar and sulfite metabolism. These are the processes that help in fragmentation and preservation of beer, the Los Angeles Times reported.

Researchers said that tinkering with yeast might lead to production of  lager or wine with better taste. The study was published in the journal Proceedings of the National Academy of Sciences on Monday.