Changes of some thermal and physical properties in model systems simulating an alcoholic fermentation

Highly simplified model systems, simulating the fermentation of 25.00% sugar-water mixture into a 12.78% ethanol-water mixture, were considered in order to study their thermo-physical properties. Calorimetric data, viscosity and water activity determinations showed that important thermal and physical changes are associated with the steps of a fermentation process. Besides the increase in ethanol content, other concomitant changes are a strong increase in ethanol vapor pressure and a decrease in water activity and viscosity. DSC measurements of the models during scanning from -140C to 25C showed three peaks: peak I (exotherm) covered a temperature range from -110C to -80C and was attributed to the recrystallization of the ethanol monohydrate; peak 2 (endotherm), with peak temperature around -70C, was attributed to the melting of the alcoholic monohydrate; peak 3 (endotherm) in the higher temperature range from -30C to OC, was due to ice melting. The alcoholic monohydrate appeared only in the final simulated step of the fermentation, where only ethanol and water were present. The inhibitory effect of even small amounts of sugars on the formation of the monohydrate might be related to the increase in viscosity. This would confirm the formation of the ethanol hydrate as kinetically hindered, as it is reported in the literature.