The lager was originally brewed in Europe, but the yeast needed to make it had not been found there until recently.
For the first time in Europe, the elusive ancestor to the modern lager yeast has been discovered. The discovery of this species in Irish soil indicates that the yeast was in Europe at the time of the switch to lager-style brews, which occurred towards the end of the Middle Ages.
Ales and stouts were the first beers brewed in Europe, not today’s popular lagers. Ales are fermented using Saccharomyces Cervisiae, which is also known as brewer yeast. This yeast is still used today in ales, stouts, and bread. When European beer makers had to switch from brewing during warmer months to cooler ones to reduce bacteria, their yeast species changed.
“We know there was a change in the species of yeast that carried out the fermentation,” says Geraldine B. from University College Dublin, Ireland. It was not Saccharomyces Cerevisiae but a new organism called Saccharomyces Pastorianus. This is the same yeast that’s used today in lagers.
In the 1980s, researchers discovered that the yeast responsible for lager production has two species of ancestors: S. Saccharomyces aubayanus and cerevisiae. This latter strain was discovered in the Patagonian Andes in 2011 but has since been found in North America.