Lager’s mystery ingredient found

Missing ancestor of yeast used in cold-brewed beer is identified

Lager beers got their start in Bavaria, but it was a little South American spice that really kicked things off.

Galls — growths resulting from a fungal infection — grow on southern beech trees in Northern Patagonia. Scientists recently found a wild yeast that gave rise to a hybrid yeast used to brew lagers in such galls on trees growing in and near two national parks in Argentina. Diego Libkind

Scientists have known for decades that a hybrid species of yeast, Saccharomyces pastorianus, is the microbe that ferments lagers. It’s also well known that one parent of S. pastorianus is the common baking and brewing yeast Saccharomyces cerevisiae. But the other parent of lager yeast has eluded scientists, who have scoured Europe and North America looking for it.

Turns out they were looking in the wrong hemisphere. An international team of researchers led by Chris Todd Hittinger of the University of Wisconsin–Madison and Diego Libkind of the Argentinean National Council for Scientific and Technical Research in Bariloche has tracked the missing wild parent of lager yeast to the beech forests of Patagonia. The researchers report the capture of the newly discovered yeast, dubbed Saccharomyces eubayanus, online the week of August 22 in the Proceedings of the National Academy of Sciences.

“I got chills reading [about] it, I was so excited,” says Barbara Dunn, a comparative geneticist at Stanford University who has been on the trail of the wild yeast herself. “It is incredibly surprising that it is from Patagonia.”

Libkind found S. eubayanus in galls — pale peach, balloonlike structures resulting from fungal infections — on Patagonian beech trees. The galls, full of sugar, house S. eubayanus and another wild yeast that ferment the sugars. It’s generally chilly in Patagonia, just the way lager yeast like it. Lagers are brewed at 4° to 9° Celsius (39° to 48° Fahrenheit).

The S. cerevisiae yeast used for making ales, wines and other alcoholic beverages don’t like the cold, preferring temperatures of about 15° to 25° C (59° to 77° F). So when Germans started brewing beers in the winter to avoid summertime contaminants such as molds, bacteria and other things that skunk beer, the new brewing conditions would have favored the creation of a hybrid lager yeast based on S. cerevisiae and a cold-loving relative, says Antonis Rokas, an evolutionary biologist at Vanderbilt University.

The surprise is where that partner came from. Bavarian brewers started making cold-brewed beers in the 15th century, before Columbus crossed the Atlantic (although the lagers didn’t have a big breakout in popularity until much later). S. eubayanus probably hopped a ship for Europe sometime early in the 16th century. The researchers aren’t sure exactly how S. eubayanus got to Bavaria; perhaps by hitching a ride on pieces of beech wood or barrels made of beech, or on fruit or even in the belly of a fruit fly. However it got to Europe, when S. eubayanus arrived it found a ready-made niche and a partner to merge with, Rokas speculates.

It’s also possible that S. eubayanus lives or lived in some forgotten pocket of the Old World, Hittinger says. “Obviously we haven’t searched every habitat on the entire globe.”

Knowing the identity of the wild parent may help scientists learn how the lager hybrids formed and how domestication genetically changed the yeast, Rokas says. Brewers may also be able to create new hybrid strains that can be tailored for modern brewing practices.

Tina Hesman Saey is the senior staff writer and reports on molecular biology. She has a Ph.D. in molecular genetics from Washington University in St. Louis and a master’s degree in science journalism from Boston University.

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