Flocculation

Flocculation is the tendency for yeast cells to clump together. When the clumps reach critical mass, they drop to the bottom of the fermentor, clarifying the beer. Some kinds of yeast do this more than others: British ale strains readily clump together, while German Hefeweizen yeast likes to remain in suspension. Flocculation is generally considered the end of fermentation, but flavors may continue to evolve for some time.