Thermal Properties of Ethanol Aqueous Solutions and Aged Spirits at Low Temperature (Studies on Aged Spirits and Their Physicochemical Characteristics. Part II)

Abstract

The previous paper on NMR spectrum of aged spirits demonstrated the formation of stable molecular clusters in which migration of ethanol molecules was restricted, and there was a decrease in monomeric ethanol, which produced a stimulative taste. In the present study, the thermal properties of ethanol aqueous solutions and aged spirits were investigated by differential scanning calorimetry (DSC). The DSC thermogram was measured at the temperature range from 150°C to 20°C. Three peaks (peak numbers l-3) were observed in the thermogram of melting aged spirits and ethanol aqueous solutions. Peak 1 (endotherm) occurring in the temperature range from 27° to 0°C mainly concerned the heat of fusion of ice and of dissolution of water to ethanol aqueous solution (ethanol conc. 0-34%), the heat of fusion of water bound to ethanol molecule (ethanol conc. 34-70%) and the heat of fusion of water solidified in a glassy state (ethanol conc. above 70%). Peak 2 (endotherm) occurring in the temperature region from 65° to 47°C concerned the heat of fusion of free ethanol (ethanol conc. 0'-34%, near 72.8%), the heat of fusion of ethanol bound to water molecule (ethanol conc. 34-70%) and the heat of fusion of ethanol solidified in a glassy state (ethanol conc. above 72.8%). Peak 3 (exotherm) occurred at 84°C and was concerned with the heat of recrystallization of the ethanol-water mixture. In aged spirits, the heat calculated from the area of peak 2 was smaller compared to new spirits and decreased in proportion to the length of storage. The effects of minor chemical components on changes in the DSC thermogram were slight. © 1985, Japan Society for Bioscience, Biotechnology, and Agrochemistry. All rights reserved