Evolution of Lager Yeast - Mom Was an Ale

The parents of lager yeast? Ale yeast:

It all started with some unhappy Bavarians. Dissatisfied with the quality of beer brewed in the summer months, they forbade brewing the beverage when the weather was warm. However, colder winter temperatures inhibited fermentation by the ale yeast that had been used for hundreds of years and fostered an unlikely pairing with a second, heartier species-producing an unusual crisp, clear brew that became today's lager.

Sherlock, an assistant professor of genetics, and Barbara Dunn, PhD, a senior research associate at the medical school, studied the genetic sequences of 17 unique lager yeast strains from breweries in Europe and the United States. They used customized DNA microarrays capable of analyzing the relative contribution of each parent, combined with limited DNA sequencing, to determine that the hybridization event actually occurred not once, as previously speculated, but twice. This genetic encore suggests that each partner brought specific, unique advantages to the match.

"It's possible that the ale strain provides a certain flavor profile, while the second strain conferred the ability to ferment at cooler temperatures," said Dunn. "Mixing them together is a nice way for the yeast to double its genetic options...."

As often happens, the offspring of such an unconventional union exhibited abnormal amounts of genetic material. Sherlock and Dunn believe that one lineage began with approximately equal amounts of each yeast's genome, whereas the other has between two to three more times S. cerevisiae than S. bayanus DNA. Studying the spread of the two groups provides a genetic snapshot of lager brewing in Europe during the past 600 years: one lineage is associated primarily with Carlsberg breweries in Denmark and others in what is now Czechoslovakia, while the other group localizes to breweries in the Netherlands, including Heineken.

Hat tip: John.