Simultaneous saccharification of starch from whole-wheat flour and fermentation to lactic acid (SSF) was investigated. For saccharification the commercial enzyme mixture SAN Super 240 L, having alpha-amylase, amyloglucosidase and protease activity, was used, and Lactococcus lactis ssp. lactis ATCC 19435 was used for the fermentation. SSF was studied at flour concentrations corresponding to starch concentrations of 90 g/l and 180 g/l and SAN Super concentrations between 3 mu l/g and 8 mu l/g starch. Kinetic models, developed for the saccharification and fermentation, respectively, were used for simulation and data from SSF experiments were used for model verification. The model simulated SSF when sufficient amounts of nutrients were available during fermentation. This was achieved with high wheat hour concentrations or with addition of yeast extract or amino acids. Nutrient release was dependent on the level of enzyme activity.