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Lager yeast

Last week, I attended an excellent seminar by Chris Hittinger on the identification and evolution of lager yeast (see the paper), part of my favorite seminar series, on evolution.

[Forgive me if this description is not fully accurate.] Ales are the original (proper, better tasting) type of beer; they’re brewed at a warmer temperature, with “top-fermenting” yeast (the yeast rises to the top or is suspended throughout the column). Lagers were developed in the 15th century in Bavaria and are brewed at a colder temperature, with “bottom-fermenting” yeast (the yeast settles to the bottom). Lagers spread world-wide in the 19th century, and now are the most popular fermented beverage (but that’s mostly swill).

(Chris explained the top vs bottom business: it has to do with flocculation genes; lager yeast clumps together and drop out of the suspension. Flocculation is different than precipitation; the latter concerns the case that the substance is first dissolved in the liquid rather than merely suspended.)

The yeast for brewing ales is Saccharomyces cerevisiae; it’s apparently long been known that lager yeast is a hybrid between the ale yeast and something else, but the origin of that something else has not been known. Previous efforts to identify it have not been successful.

Chris and colleagues (the SSS Consortium) sought to expand the known yeast species by gathering new strains in the wild on five continents. As part of that effort, they identified a new species in Argentina, adapted to fermenting in cold temperatures, that turned out to be the missing part of the hybrid that formed lager yeast. They believe that the yeast was brought from South America to Bavaria sometime after the 15th century (when lagers were first developed) but before the 19th century (when they became widespread).

Who would have thought you’d have to go to Argentina to figure this out?

Chris mentioned that he prefers lager, while his former postdoc advisor, Mark Johnston, prefers ales, and that they’ve had more debate on that point than on the science. I agree with Mark.