A widespread interest has been noted in continuous-power ethanol fermentation utilizing systems with strong biomass accumulation. Flocculent yeast systems require not additional mechanical complexity to reach biomass levels on the order of 60-90 g/L. This is achieved by coupling a decantor to a fermentor, taking advantage of the fact the flocs may easily settle. the general performance of yeast floc reactors have been established: the high biomass levels achieved allow efficient ethanol conversion (40-80 g/L) and high productivities (10-18 g/L h) for 100-190 g/L glucose concentration in the feed with practically total conversion of substrate. The present communication gives additional information on the kinetics of a continuous flocculent yeast reactor operating under transient conditions. We give insight into the optimization of the startup operation.