Yeast & Fermentation

Who invented lager yeast? No one—and that's the most common misconception. Emil Christian Hansen isolated the first pure culture of a bottom-fermenting yeast at the Carlsberg Laboratory in 1883, dubbed "Unterhefe Nr. I." It was the very same yeast strain that Jacobsen had received from Spaten in Munich back in 1845.

What was new was the method Hansen used to cultivate the yeast. He started from a single cell and kept it free of contaminating organisms. Before this, pitching yeast often harbored bacteria and wild yeasts, causing some brews to fail. In November 1883, the pure-culture yeast was used in commercial production in Copenhagen for the first time.

The yeast was named Saccharomyces carlsbergensis after the brewery. Today, lager yeast is classified as Saccharomyces pastorianus. It's a cross—more precisely a hybrid—between the top-fermenting brewer's yeast Saccharomyces cerevisiae and the species Saccharomyces eubayanus.

This second species was described in 2011 in Patagonia. That doesn't mean lager yeast originated in Patagonia, though—the parent strain was simply discovered there first and was later also found in Tibet and North America.

Bottom-fermenting yeast works cool, at temperatures from just above freezing up to about ten degrees Celsius, and settles at the bottom of the tank once fermentation finishes. The beer then matures for weeks in a cold lagering tank. During this time, it clarifies and develops a rounder character.

The craft scene, by contrast, mostly brews with top-fermenting yeast, at higher temperatures and with shorter maturation times. This holds true for Nørrebro Bryghus's pale ales as much as for many Mikkeller beers. Their yeast strains contribute fruity aromas that a lager simply doesn't have.