Modern lager arose when a beer and an ale met in a Munich brewhouse

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If you like lager, chances are you’ve got a 17th century brewmaster to thank for it. The commercial yeast used to brew most modern lagers was created when the pasty yeast slurries for a white ale and a brown beer mixed in a cellar of  the original Munich Hofbräuhaus—not to be confused with the beer hall there today—sometime between 1602 and 1615, according to a new synthesis of historical brewing records and genetic histories of yeast.

Today lager accounts for 90% of all beer sold; ales, made with different yeasts, make up the rest. Nonetheless, the origin of lager has been “shrouded in mystery for many years,” says yeast biotechnologist John Morrisey of University College Cork. The Hofbräuhaus scenario is “definitely plausible,” says evolutionary biologist Brigida Gallone of Naturalis Biodiversity Center, who was co-author of a key genetics study.

Although 17th century brewmasters didn’t know about the existence of yeast, they did notice the new blend was a winner—it fermented vigorously like an ale but tolerated colder temperatures, like a brown beer. This meant they could brew a clean-tasting lager earlier in the spring in the Northern Hemisphere, where temperatures plummeted during the Little Ice Age, from about 1300 to 1850 C.E. Eventually, one yeasty starter from the new brew was taken by stagecoach to Copenhagen, Denmark. There, in 1883, Emil Christian Hansen, a mycologist at the Carlsberg Research Laboratory, purified this hybrid yeast, named Saccharomyces pastorianus in honor of the French chemist Louis Pasteur.

Hansen’s purified strain revolutionized beer production because brewers could consistently make high-quality, safe lager from every batch. Before that, wild strains of yeast sometimes contaminated the slurries, causing “beer sickness” and gastrointestinal distress. The purified version of S. pastorianus was so successful that it quickly replaced older yeast strains and is still used in most lagers today.

A major clue about its origin came in 2016 when researchers compared the genomes of 120 strains of lager and ale yeasts to sort out their family tree. They sorted out the details of how S. pastorianus, a hybrid species, formed when two yeast species met: S. cerevisiae from wheat ales and S. eubayanus, used for brewing brown beer made from barley and hops. Using a molecular clock, they estimated that the hybrid originated sometime in the mid–16th century, microbial geneticist Kevin Verstrepen of the VIB–KU Leuven Center for Microbiology and his colleagues reported in 2019 in Nature Ecology & Evolution. It likely hailed from Bavaria, because the S. pastorianus in lager has segments of DNA from its parent yeast S. cerevisiae that most closely match Bavarian strains of that yeast.

Inspired by the results, Technical University of Munich brewing microbiologist Mathias Hutzler, late biochemist Franz Meußdoerffer, and brewing scientist Martin Zarnkow scoured historical records from breweries and books in Old German for clues to where the two yeasts could have mixed. They also looked for samples of old yeast in brewery cellars across Bavaria, but yeast is notoriously short-lived and seldom survives more than a few years if not frozen.

They pieced together a detailed historical account that described a Bavarian duke Maximilian, who seized brewing rights for a white wheat ale from a Bohemian aristocratic family in 1602, then brought the yeast and a brewmaster who could make white ale to his Munich Hofbräuhaus. The account noted that the Hofbräuhaus was the only brewery in Bavaria at the start of the 17th century allowed to make large amounts of “top-fermenting” white ale—so-called because of the fluffy foam that forms on top of the slurry in ale. (In “bottom-fermenting” lagers, the yeast ferments more calmly and settles at the bottom of the vessel.) In the 16th century, Bavarian beer purity laws required breweries to make bottom-fermenting beers from barley and hops during cold spring months to preserve wheat for breadmaking when food was scarcer.

From 1602 to 1607, brewmasters from Schwarzach in lower Bavaria and Einbeck in Lower Saxony—along with their yeasts—were active in the Munich Hofbräuhaus, which no longer exists. The records show that “bottom fermented and top fermented beer was produced side by side under one roof,” Hutzler reports today in FEMS Yeast Research. There, S. cerevisiae yeast from white ale may have mixed and mated with S. eubayanus yeast from brown ale to form S. pastorianus. “The amazing thing,” he says, “is the history fits perfectly with the genetics.”

Verstrepen, senior author of the earlier genetics study, adds: “The historical data that Mathias gives is compelling; we know that the hybridization happened around Munich around that time and in a brewery.” The hypothesis “makes sense,” he says, but it’s hard to prove. Gallone cautions, for example, that the molecular clock date is a rough estimate.

As brewers turned almost exclusively to S. pastorianus to make lager, much of the world’s yeast diversity was lost. Several teams are making new hybrids to resurrect traits such as the genes that allow S. cerevisiae to ferment at higher temperatures, says geneticist Chris Hittinger of the University of Wisconsin, Madison. “Maybe you can save money on the energy costs to brew lager at cold temperatures,” Hittinger says. That would transform a beer fit for the Little Ice Age into one suited for the tastes—and energy requirements—of the modern era.

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