Effect of pressure and temperature on alcoholic fermentation by Saccharomyces cerevisiae immobilized on γ-alumina pellets.

Saccharomyces cerevisiae was immobilized on γ-alumina pellets and used for repeated batch fermentations in glucose medium (16.5 g/100 mL) at various temperatures and pressures. An increase in pressure from 3 to 7 atm and a decrease in temperature from 30 to 20 °C reduced the ethanol productivity by about 50% and 70%, respectively. Increasing concentrations of volatile by-products were observed at lower fermentation temperatures, while the pressure influence on the concentrations of these by-products was proved to be more complex. Mathematical expressions were established to allow the calculation of the fermentation rate at various pressures and sugar concentrations when the corresponding rate at atmospheric pressure is known. The study showed that the height of bioreactors has to be limited to 19.5 m due to hydrostatic pressure shock at higher fill levels.