- $12 for two Groupons, each good for $10 worth of beer ($20 total value)
Brewing Yeast: The Sweet Strains of Fermentation
Brewmasters strike a delicate balance with every batch of beer that they create. Learn more about one of their key ingredients.
To understand what yeast does for beer, it’s helpful to consider what beer would be like without it: cloudy, flat, and sweetly bland. Beer in this inchoate state has a name—it’s wort, a boiled mixture of malt extract, water, hops, and the brewer’s hopes and dreams. The job of the single-celled microorganisms known as yeast? Eat the sugars in this mixture, turning them into bubbly carbon dioxide, alcohol, and other compounds that add flavor.
North, South, and Yeast
This is more or less how all yeasts work, but brewing yeast is special due to what happens next: flocculation. As the yeast nears the end of the fermentation process, the cells form clumps and either drop to the bottom of the vat or rise to the top. This spent yeast can be skimmed away, leaving beer that is more or less clear depending on the desired style. (Most commercial beers are further filtered before they reach the bottle or keg.) Top-fermenting or ale yeasts rise to the surface of the wort during fermentation; they’re used to craft ales, porters, stouts, and wheat beers, among others. Bottom-fermenting yeasts, on the other hand, are part of what gives lagers their mellow character.