Patagonian galls such as these harbor the cold-adapted yeast Saccharomyces eubayanus, a parent of the hybrid yeast used to make lager or cold-brewed beer. A field survey has confirmed that the parent yeast S. eubayanus, which somehow made its way to Bavaria 500 or so years ago, is easily isolated in Patagonia. A Wisconsin team recently isolated the yeast, although at low frequency, near Sheboygan, Wis. — the first time it has been found in nature in North America.
And how did it travel to Bavaria hundreds of years ago? OK, this story from 
the University of Wisconsin, Madison on the mysterious origins of bottom-fermenting lager yeast is a little “inside baseball” — for the anorak brigade, as the Brits might say — but it is interesting to brewers and beer lovers.
SCIENTISTS FIRM UP ORIGIN OF COLD-ADAPTED YEASTS THAT MAKE COLD BEER
MADISON, Wis. — As one of the most widely consumed and commercially important beverages on the planet, one would expect the experts to know everything there is to know about lager beer.
But it was just a few years ago that scientists identified the South American yeast that, hundreds of years ago, somehow hitched a ride to Bavaria and combined with the domesticated Old World yeast used for millennia to make ale and bread to form the hybrid that makes lager or cold stored beer.
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