Pouring beer. Credit: Sarah Whyman

What happens when you combine a cold-loving yeast that grows on beech trees in Patagonia with a room temperature-loving yeast from Europe? Lager happens.

For millennia, the yeast Saccharomyces cerevisiae has been fermenting fruit and grains into wine, cider and ale, but lager didn’t appear on the scene until the 1400s — and it was by accident. Bavarian monks were storing beer barrels in caves when an unknown yeast combined with Saccharomyces cerevisiae to create the first batch of lager.

Over the years, lager has been produced using the fully domesticated yeast Saccharomyces pastorianus, which is a hybrid of Saccharomyces cerevisiae and the unknown — until now — yeast.

In a discovery described in the Proceedings of the National Academy of Sciences last month, scientists have identified a new species of South American yeast, Saccharomyces eubayanus, that appears to be the previously unknown yeast responsible for helping create lager. While scientists can’t definitively say how the Patagonian yeast found its way to Bavaria, a fruit fly or piece of wood is most likely responsible.

Bonus fact: Wondering what the difference is between ale and lager? As this article illustrates, it’s all about the yeast. Saccharomyces cerevisiae is a relatively fast, top-fermenting yeast that works best in warm/room temperature environments to produce ale, while lager is produced with bottom-fermenting yeast that prefers cooler temperatures and need longer fermentation time. Ales are served warm, lagers are served cold, and the world enjoys its beer — although more of it prefers lagers over ales.

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