What do you call the foam cap formed during fermentation?

The correct term for the foam cap formed during fermentation is "Krausen." This frothy layer consists of yeast, proteins, and hop residues that rise to the surface during the fermentation process, particularly in the production of beer. The krausen plays a vital role, as it indicates that fermentation is actively occurring and helps protect the beer from oxidation and other contaminants within the fermentation vessel.

Other terms might refer to different aspects or elements within the fermentation process but do not specifically denote the foam cap itself. For instance, "yeast head" is less commonly used and may not accurately describe the phenomenon, while "fermentation cap" and "bubble cap" are not standard terminology.