Kräusen, also spelled "kraeusen" or "krausen", pronounced "KROY-zen", is a beer

Beer

Beer is the world's most widely consumed andprobably oldest alcoholic beverage; it is the third most popular drink overall, after water and tea. It is produced by the brewing and fermentation of sugars, mainly derived from malted cereal grains, most commonly malted barley and malted wheat...

-brewing

Brewing

Brewing is the production of beer through steeping a starch source in water and then fermenting with yeast. Brewing has taken place since around the 6th millennium BCE, and archeological evidence suggests that this technique was used in ancient Egypt...

 term that has two definitions in that context.

1. A method to carbonate beer in which wort

Wort

Wort may refer to:* Wort, the liquid created by the mashing of malted barley to use in brewing beer* Worting, Hampshire, a large district and suburb of the town of Basingstoke, in Hampshire, England....

 is added to the fermented/finished beer to carbonate.

2. The foamy, meringue

Meringue

Meringue is a type of dessert made from whipped egg whites and sugar, occasionally some recipes may call for adding an acid such as cream of tartar or a small amount of vinegar and a binding agent such as cornstarch found in icing sugar which may be added in addition to the corn starch which...

-like head that develops during the initial stage of beer fermentation.

The word comes from German for frizzy hair ("krauses Haar"). The foam buildup is attributed to yeast eating sugars and building up CO2 in the process.