Continuous pH measurements were performed during the yogurt fermentation process. Various conditions of dry matter fortification, heat treatment of the base milk, starter culture, and incubation temperature, were included in the experiments. The pH profiles with incubation time were described on the basis of the modified Gompertz equation for bacterial growth. The four parameters of the equation were used to evaluate the effects of the different process conditions. Dry matter fortification did not affect the pH development. Sterilization of the base milk enhanced the pH development. Incubation temperatures that were lower than the optimal one, caused the pH development to slow down. Inoculation with a ropy strain starter culture yielded a different shape of the pH profile with time. The lag time for pH decrease and the maximal pH decrease with time, reflected the intended acidification rates of the involved starter cultures.