LAUSR

Water activity (aw) is an important property of foods, with correlations to safety, quality, and shelf-life. The presence of high concentrations of non-water volatiles has been problematic for analytical aw instruments, thereby limiting potential applications of aw measurements for quality assessments of fermented beverages and foods. The objectives of this study were to measure the aw values (aws) of wines and spirits using a tunable diode laser instrument (AquaLab TDL, METER Group, Inc.), reported to be unaffected by volatiles such as ethanol, and determine the effects of ethanol and residual sugar (R.S.) concentrations on the aw. The aws of commercial wines (n = 678), other liquors (n = 42), and model solutions containing controlled concentrations of ethanol and sugars were measured using the TDL at 25 °C. The alcohol by volume (ABV) was determined by electric ebulliometer and Fourier transform infrared spectroscopy (FTIR) methods, and sugars were determined using a FTIR method. The aws of wines ranged from 0.860 to 0.968 (average 0.940 aw), the aws of spirits ranged from 0.750 to 0.909 aw, and grain alcohol had the lowest aw at 0.365 and the highest ABV (95%). The Norrish equation, accounting for ethanol, glucose, fructose, and sucrose concentrations, resulted in predicted aws of wines that were 0.012 ± 0.007 higher than the measured aws. Ethanol had a greater effect on the aw of wines than sugar contents, and the ~ 0.012 lower than predicted aws of wines were attributed to the effects of additional solutes (glycerol, acids), that were not included in the Norrish equation, on lowering the aw. Graphical Abstract Graphical Abstract