The production of citric acid was achieved by using Aspergillus niger conidiaspores, entrapped in Ca-alginate beads, and the factors that affect this production were investigated. The effects of starting sucrose concentration (100-180 g/l), nitrogen concentration (0-0.3 g/l), methanol concentration (0-6 ml) and finally ethanol concentration (0-5 ml) in 100 ml feeding medium on citric acid production were studied and optimum experimental conditions were determined. The starting nitrogen concentration (0.05 g/l) and the starting sucrose concentration (140 g/l) were optimized and maximum citric acid production observed under these given conditions. Maximum citric acid production was observed upon addition of 4.0 ml methanol and 3.0 ml ethanol. (C) 2004 Elsevier Ltd. All rights reserved.