Wednesday, September 7, 2011

Yeast Geneology

(Image: S cerevisiae under DIC microscopy, via Wikimedia Commons user Masur)

At the Smithsonian food blog, Food & Think, there is an interesting bit about the origin of lager yeast.

As you may know, most beer we drink is brewed with a species of yeast called Saccharomyces cerevisiae. Depending on the type of beer, a different strain of this yeast is used. For ales, brewers use a strain of ale yeast, which ferments more or less at normal room temperatures (15-20C) and is known as top-fermenting yeast. For a lager, one would use a lager yeast, which is a bottom fermenting yeast that functions at cooler temperatures (around 5C). Additionally, lager yeast is able to digest raffinose, a sugar present in wort (unfermented beer) that ale yeast cannot ferment. This means that lager yeast can contribute to a higher sugar-to-alcohol conversion and results in a less sweet beer.

Previously, scientists had compared the genomes of lager and ale yeast and found that lager yeast resulted from a cross between S. cerevisiae and another type of yeast. Recently, this type of yeast, which was previously undescribed, has been identified, as described in a recent paper in PNAS. Interestingly, this yeast is native to South America, suggesting that modern lagers (even European ones) owe many qualities to a species of New World yeast. Previous to the European exploration of the Americas, lagers in Europe may have been brewed with unhybridized S. cerevisiae, resulting in a different beverage than what we identify as lager beer today.

It seems that globalization hasn't been such bad news for beer, after all.

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