Enhanced ethanol production in multiple batch fermentations with an auto-flocculating yeast strain

An auto-flocculating strain of S. cerevisiae was used to carry out multiple batch fermentations at high cell concentrations to produce ethanol using glucose, sucrose or sugar cane juice as carbon source. Typical improvements in average volumetric ethanol productivity of 4-6 fold were achieved over conventional batch fermentation. A gradual decline in specific ethanol productivity was observed as the cycle number increased, dictating the maximum cell residence time in the system. Because of the low capital expenditures involved, the approach is promising as a means of upgrading existing distilleries. The effects of providing external agitation and of maintaining a low dissolved oxygen concentration on the fermentative ability of the auto-flocculating yeast were also measured. Increased levels of agitation were found to improve ethanol productivity by maintaining flocs of smaller mean size. As expected, the presence of a low dissolved oxygen concentration led to higher specific and volumetric ethanol productivities at the expense of slightly lower product yields