In my pending U.S. application Ser. No. 497,306 filed Aug. 14, 1974, now U.S. Pat. No. 3,947,323 there is described the formation of amylase in an aqueous culture containing Aspergillus niger, a nutrient therefor and a small quantity of a polymeric material selected from a carboxypolymethylene, a polyacrylate and a polyethylene glycol. The presence of the polymeric material improves the microbial growth rate and the rate of product formation while the polymeric material is not consumed in the process.