Yeast flocculation: kinetics and collision theory.

Flocculent yeast cells have an absolute requirement for mechanical energy input in order for flocculation to occur. Flocculation is arrested by cessation of energy input. The initial rate of flocculation increases as the square of the cell concentration. There is a minimum shaking speed to initiate flocculation and thereafter the initial rate of flocculation increases exponentially with the shaking speed. The minimum shaking speed for flocculation to occur increases with pH value. Activation energy for flocculation, derived from Arrhenius-like plots, varies with pH value. We propose that activation energy is required to overcome mutual repulsion between charged yeast cells and allow flocculent bonds to be formed.