Corn starch was hydrolysed by glucoamylase (EC 3.2.1.3, 1,4-a-D-glucan glucohydrolase) in a chemostat; 106 g L-1 reducing sugar was produced at 40 degrees C after 46 h, whereas only 42 g L-1 was produced at 30 degrees C. When corn starch concentration was increased from 64.6 g L-1 to 161.5 g L-1, the amount of reducing sugar produced increased with the initial substrate concentration. The studies show that there is a product concentration (p(0)) above which product inhibition becomes apparent. A new model for starch hydrolysis considering the product inhibition point is presented. (c) 2006 Society of Chemical Industry.