Flocculation refers to a yeast strain’s tendency to clump together and drop out or fall out of suspension to the bottom of the fermenter or holding vessel. As yeast flocculates, the beer begins to clarify. Some yeast strains tend to have high flocculation, such as Wyeast Scottish – 1728, while other strains like Wyeast American Wheat – 1010 have very low flocculation. The physical appearance of the yeast cell plays a big part in its flocculation level.
It is important to choose a yeast with an appropriate flocculation profile when designing a beer; for instance you would not pair a Belgian Wit wort with a high flocculation yeast, as you want some of the yeast to stay in suspension in the finished beer.