Dough fermentation is a process very similar to the expansion of a pseudoplastic foam, in which initial germs (yeast) are quasi-homogeneously distributed. The present model considers the expansion as a chemical reaction, which producing gas leads to the growth and the coalescence of bubbles, which form in the pseudoplastic paste, thus conferring to the loaf its final volume. The fermentation kinetic was investigated by monitoring the variation of the dough volume vs time by means of image analysis. The leavening process can be divided into three stages: the lag stage, a positive acceleration stage and a negative acceleration stage. Aim of the model developed in this study was described the variation of dough volume y as a function of time t, i.e. y =f(t). A modified Gompertz model was chosen as the best descriptive model of the leavening process. Quite good agreement was observed between experimental data and model parameters. (C) 2007 Elsevier Ltd. All rights reserved.