The direct conversion of starch hydrolysate (15 Dextrose Equivalent) to ethanol using a coimmobilizate of amyloglucosidase and Saccharomyces cerevisiae was studied in a batch stirred tank reactor. The performance of the reactor for various system parameters viz. stirrer speed, pH, initial substrate concentration and temperature has been studied. The ethanol productivity is limited by inhibition for initial substrate concentrations above 75 g/l. The optimum pH and temperature of reaction is 5.0 and 30 °C respectively. © 1992 Springer-Verlag.