Lagers in a cold climate: the yeast behind the brew

Lager bubbles

Louis Pasteur is a pretty big figure when it comes to beer, even though you might not think it straight away. We’ve talked about beers brewed with wild yeasts before, of the great sour beers that come out Belgium during the colder months that have been fermented by naturally occurring yeasts (like brettanomyces) living in and around the breweries.

This was the way that all beers were made before old mate Pasteur investigated microbiology. Pasteur lived between 1822 and 1895, and lent his name to bottles of beer and wine the world over with the term, pasteurised. It was his breakthroughs, according to Greg Duncan Powell, that led to the discovery and isolation of Saccharomyces pastorianus, otherwise known as S. carlsbegensis. Which is what? The lager yeast.

See lagers were discovered by some accident. The story goes that monks laid their lagers down in oak casks in cool caves during the warmer summer months so that they wouldn’t spoil. (Unpasteurised beer left in oak during a hot summer wouldn’t taste so great, you see.) And they made the accidental discovery that their beers would ferment.

But it took Pasteur’s discoveries to work out why that was. And it’s thanks to S. pastorianus: there’s something about its genes that means it can operate at lower temperature than cerevisiae, and it’s this low, slow fermentation is that is responsible for the clarity of lagers.


As Duncan Powell points out, though, in his book Beer, the lagers at that stage would have been darker and richer in flavour than we’re accustomed to today, given the Bavarians were using dark roasted malts. The gently roasted malt — from which a pale colour is achieved, is thanks to Josef Groll from Pilzen, but that’s another story.

So you might think of lagers as harmless, bland drinks — and a lot of the time you’d be right. But it’s not because yeast doesn’t play a big role. After all, it’s thought that the lager yeast pastorianus is  the love child of cerevisiae and a Patagonian species, S. eubayanus. Eubayanus itself is thought to have made it to Europe on the back of oak shipped out of Patagonia, and onto oak that found its way into barrels that found its way into the hands of brewers who stashed them away inside their cold caves.

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