Yeast & Fermentation

Cass, Hite, and OB Golden Lager are all bottom-fermented beers. Bottom-fermented means the yeast works at cool temperatures of around 8 to 12 degrees Celsius and eventually settles at the bottom of the tank. The beer then matures cold in the storage tank for weeks afterward, so it turns clear and smooth. This process is called lagering, hence the name lager.

The big producers work with large, closed stainless-steel tanks and tightly controlled cooling. That suits a beer meant to taste the same every time, whether poured in a riverside hof on the Han or bought at the supermarket. The yeast contributes little fruity character, letting the grain take the lead.

In the brewpubs of Gyeongnidan or Hongdae, by contrast, the tanks often stand behind glass, and top-fermented beers are brewed there too. Top-fermenting yeast works at around 18 to 22 degrees Celsius and produces more fruit esters—aroma compounds reminiscent of pear, banana, or citrus. This is how an IPA or wheat beer gets brewed, the kind familiar to guests from Canada and the US.

It's worth distinguishing this from makgeolli, which many travelers mistake for a rice beer. Makgeolli is actually a cloudy, lightly tart rice wine. Its fermentation starter is nuruk, a dried mix of mold cultures and yeasts that convert rice starch into sugar and then into alcohol. The processes for beer and rice wine are fundamentally different.

Somaek, too, involves no fermentation—it's simply a mix of soju and beer. Soju is a clear Korean spirit that, unlike beer, is distilled or fortified rather than brewed. Mixing somaek doesn't create new alcohol; yeast plays no part in it at all.