Beer School, Session 4

Top vs. Bottom Fermented Beers

While reading about different types of beer for the Beer School posts I keep coming across two terms: top fermentation and bottom fermentation. Usually this is one of the first facts given about a beer. Before I get further along in my quest for the world's best brew I need to understand these terms.

All beer is made from the same basic things: water, malt, hops, and yeast. Fermentation is the key process by which these ingredients are turned into beer. During fermentation the yeast breaks down the carbohydrates and produces alcohol. The byproducts of this process are what give different types of beer their unique flavor and characteristics.

There are two main varieties of yeast used in beer making: lager and ale. Top-fermentation happens with ale yeast. It was used to create the first beers since fermentation takes place in warmer temperatures. As the name indicates, the yeast acts on top of the brew. Top fermented beers often have higher alcohol concentrations then bottom fermented varieties and a fruity, sweet taste.

Bottom-fermentation, which used lager yeast, happens at lower temperatures. The yeast settles to the bottom of the brew and more sugars are fermented. The resulting beer has a crisp, clean taste.