kräusen

Kräusen, also spelled kraeusen, is a German brewing term referring to the active, frothy foam that forms on top of fermenting beer. It is a visible sign of vigorous fermentation, where yeast consumes sugars and produces carbon dioxide and alcohol. This foam is characterized by its bubbly, often white or off-white appearance, and can range in texture from creamy to airy.

The presence of kräusen indicates that the primary fermentation is underway. Brewers often monitor the kräusen for signs of fermentation activity, such as its height, color, and texture. A healthy kräusen typically rises and then gradually recedes as fermentation slows and the yeast settles.

In some traditional brewing practices, particularly for certain lagers, brewers may intentionally collect kräusen from a primary fermentation and pitch it into a new batch of wort. This process, known as kräusen-pitching or krausening, is a method of using actively fermenting yeast to initiate fermentation in a new batch, often resulting in a naturally carbonated beer with a cleaner flavor profile. This technique can also contribute to a beer's clarity and complexity.