Lager-brewing yeast was probably born twice

Genome of newly discovered parent species shows strains are separate crosses. Lager isn’t just a beer style, it’s a yeast lifestyle. Humans have been brewing with ale yeast—Saccharomyces cerevisiae—for thousands of years. But it was less than 600 years ago that European brewers stumbled on lager yeast.

http://arstechnica.com