A new strain of the yeast Metschnikowia koreensis was grown in shake flasks and a stirred bioreactor for the production of carbonyl reductase. The optimal conditions in the bioreactor for maximizing the biomass specific activity of the enzyme were found to be: a medium composed of glucose (20 g/L), peptone (5 g/L), yeast extract (5 g/L) and zinc sulfate (0.3 g/L); the pH controlled at 7; the temperature controlled at 25 degrees C; an agitation speed of 500 rpm; and an aeration rate of 0.25 vvm. In the bioreactor, a biomass specific enzyme activity of 115.6 U/g(DCW) was obtained and the maximum biomass concentration was 15.3 g(DCW)/L. The biomass specific enzyme activity obtained in the optimized bioreactor culture was 11-fold higher than the best result achieved in shake flasks. The bioreactor culture afforded a 2.7-fold higher biomass concentration than could be attained in shake flasks. (C) 2011 Elsevier Ltd. All rights reserved.