High Kräusen

High Kräusen, also known as the growth phase, is what most of us think of as “active fermentation.” This is when yeast rapidly consumes wort sugars and converts them to carbon dioxide and alcohol.

This is also the most visually arresting portion of the fermentation cycle. A thick, fluffy white foam (Kräusen) appears on top of the beer, flecked with brown bits of hops and other wort sediment. If fermentation is taking place in a transparent vessel like a carboy, streams of carbon dioxide bubbles can be seen rising up the sides, and the airlock or blowoff will vigorously release gas.