A biochemically structured model has been developed to describe the continuous fermentation of lactose to ethanol by Kluveromyces marxianus and allowed metabolic coefficients to be determined. Anaerobic lactose-limited chemostat fermentations at different dilution rates (0.02-0.35 h(-1)) were performed. Species specific rates of consumption/formation, as well as yield coefficients were determined. Ethanol yield (0.655 C-mol ethanol*C-mol lactose(-1)) was as high as 98% of theoretical. The modeling procedure allowed calculation of maintenance coefficients for lactose consumption and ethanol production of m(s) = 0.6029 and m(e) = 0.4218 (C-mol) and (C-mol h)(-1), respectively. True yield coefficients for biomass, ethanol and glycerol production were calculated to be Y-sx(true) = 0.114, Y-ex(true) = 0.192 and Y-sg = 2.250 (C-mol) and (C-mol)(-1), respectively. Model calculated maintenance and true yield coefficients agreed very closely with those determined by regressions of the experimental data. The model developed provides a solid basis for the rational design of optimised fermentation of cheese whey. (C) 2012 Elsevier Ltd. All rights reserved.