A simple fed-batch system for cultivating genetically engineered yeast generating lactate under the regulation of the PDC1 promoter was established. Traditional strategies that avoid occurrence of Crabtree effect, such as respiratory quotient (RQ) control or ethanol control, are not applicable to the strain because of reduced generation of ethanol and CO2 by-products. In this system, the feed rate increased when the pH was >5.0, and decreased when the pH was <5.0. Using this system, cell yields on sucrose increased by approximately 30% compared to that with the conventional RQ control method, due to the early detection of occurrence of Crabtree effect by pH decrease. (C) 2012, The Society for Biotechnology, Japan. All rights reserved.