Continuous alcoholic fermentation of sucrose using flocculating yeast. The limits of invertase activity

Summary At high flow rates, the continuous alcoholic fermentation of sucrose in a laboratory fermenter with internal cell recycle, using a strongly flocculating yeast can be limited by the substrate hydrolysis. This system is sensitive to glucose catabolic repression and to mineral deficiency. The release of invertase activity in the medium is negligible. From theoretical and experimental considerations, the hydrolysis rate is imposed by diffusionnal limitations in the biomass particles. Nevertheless, ethanol productivities as high as 68 g/L.h can be reached, without biomass retention problems. A better understanding of the basic phenomena involved in floc formation and evolution is required to control reactor performances.