Yeast & Fermentation

Why does Patagonia have a place in the world's beer history? Because of a fungus on tree bark. In 2011, a team led by Argentine researcher Diego Libkind described the yeast Saccharomyces eubayanus in the journal PNAS. It was found in the southern beech forests of Nahuel Huapi and Lanín National Parks.

Here's what makes it special: the yeast used to brew lager today is called Saccharomyces pastorianus, a hybrid—meaning a cross between two species. One parent is the common brewer's yeast Saccharomyces cerevisiae. The other parent remained unknown for a long time, until it was found in Patagonia: Saccharomyces eubayanus matched 99.5 percent of the missing genetic portion of lager yeast.

That doesn't mean lager yeast originated in Patagonia. The parent strain was simply discovered there first. Researchers later found it in Tibet and North America as well, and exactly where and when the cross with brewer's yeast occurred remains a subject of ongoing research. Brewers in Bariloche and El Bolsón don't brew any differently because of this discovery, but it's certainly a point of local pride.

In everyday brewing, something else dominates instead. Pale Ale and IPA are top-fermented, meaning the yeast works at room temperature—around 18 to 22 degrees Celsius—and rises to the top as it works. After one to two weeks, most of the sugar has fermented out, and the beer then matures a few more days at cooler temperatures. For heavily hopped beers, some brewers add another round of hops during this phase.

The cool mountain setting helps: Andean nights keep fermentation rooms fresh, and brewers working without large cooling systems have less heat to fight than those on the plains.