Based on a mathematical model for ethanol fermentation, the optimal pattern for changing culture temperature to maximize the final ethanol concentration was derived utilizing the maximum principle. The optimal temperature scheme started cultivation at 30 degrees C (upper limit) descending later to 20 degrees C (lower limit). The effects of culture temperature and ethanol concentration on growth and ethanol formation were studied by controlling the ethanol concentration at a specified level using recycle with a hollow fiber module. A novel method of operation was also investigated where temperature was initially kept at 30 degrees C and ethanol concentration was controlled low simultaneously by the recycle system. The culture temperature was eventually lowered and the draw-off rate through the hollow fiber stopped. This operation was shown to yield significant improvement for efficient ethanol production.