Kinetics of Grape Juice Fermentation Under Aerobic and Anaerobic Conditions

¹ DISTAM, Department of Food Science and Microbiology, University of Milan, via G. Celoria 2, 20133 Milano, Italy

Fermentation trials were carried out on grape juice under aerobic and strictly anaerobic conditions, obtained by air and nitrogen sparging, respectively. Fermentation temperature was controlled by circulating thermostatically controlled water, and a yeast inoculum rich in sterols prepared in standardized conditions was used. Kinetics of cell growth, sugar consumption, and ethanol and glycerol production were evaluated during fermentation. Experimental data were processed by nonlinear regression using the Gompertz equation, and the equation constants were obtained. Good fitting of data was obtained both for aerobic and anaerobic fermentations. Effects of aerobiosis and anaerobiosis on fermentation kinetics were evaluated; fermentation was completed within 100 hours under aerobic conditions, and glycerol production was lower than under anaerobic conditions. Sugars were exhausted within 200 hours under anaerobic conditions, obtaining a higher amount of glycerol. Number of cells reached nearly 1 x 10⁸ cells/mL in both fermentation conditions. Acetic acid and acetaldehyde concentrations were also monitored during fermentation; since experimental data were scattered, kinetics production could not be modelled. In any case, it was observed that fermentations carried out under aerobiosis produced much higher amounts of both secondary products. Sterol content of the yeast was evaluated before and after fermentation, and relevant data are given.

Key words: alcoholic fermentation kinetics, oxygen, sterols, secondary products

Submitted on August 31, 1995

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