Growth of individual microbial species, lactic acid and gas production and dough volume increase was experimentally measured and mathematically simulated during sour dough production at 25 o C with 100%, yeast, 80% yeast plus 20% L. actobacillus plantarum, 60% yeast plus 40% L. plantarum, 40% yeast plus 60% L. plantarum, 20% yeast plus 80% L. plantarum and 100% L. plantarum inoculum. Experiments were also done with 80% yeast pluse 20% L. plantarum inoculum at 20, 30, 35 and 40 o C, and the data were simulated. The results indicated that leavening was a multiphase fermentation process