Fermentation by which the the flocculating yeast rises to the surface of the liquid mixture known as the wort. In doing so, it is possible to skim the flocs of yeast from the mixture. Part of the reason for the flocs rising to the surface is due to being somewhat hydrophobic.

When talking about the setting in which top-fermentation occurs, it usually occurs in open fermenters. They also tend to occur at higher temperatures; as such, top-fermentation is associated with ales.