An optimisation study of the large-scale enzymatic synthesis of a liquid wax ester from oleic acid and oleyl alcohol using Novozym 435 was carried out. Investigations were performed in batch mode with a stirred tank reactor (STR) with one multi-bladed impeller. Response surface methodology (RSM) based on a five-level, three-variable central composite rotatable design (CCRD) was used to evaluate the interactive effects of various parameters. The parameters are amount of enzyme (A) (90-120 g), impeller speed (B) (100-400rpm) and temperature (C) (40-60 degrees C). The optimum conditions derived via RSM at a fixed reaction time of 1 h were successfully optimised as A = 104 g, B = 388.0 rpm and C = 49.7 degrees C. The actual experimental yield was 96.7% under the optimum conditions, which compared well with the maximum predicted value of 97.6%. (c) 2005 Society of Chemical Industry