Mathematical modelling of ethanol production by mixed kefir grains yeast population as a function of temperature variations

A mathematical model was developed to describe the effect of temperature and fermentation time on the kinetic parameters of ethanol production by the mixed kefir grains yeast population, using full fat cow's milk as a fermentation medium. Modified Gompertz model was used to describe this phenomenon. The kinetic parameters of the model were successfully predicted by using the least-square method. The influence of temperature on kefir grains biomass increase and microbiological composition of kefir product and kefir grains was investigated and quantified. Furthermore, Arrhenius relationship between operating temperature and the maximum ethanol production rate was established. The activation energy of ethanol production was 64.3 kJ/mol. The adopted mathematical model could describe very well the dynamics of ethanol production from the beginning up to the stationary phase during the kefir fermentation.