The aim of this study was to measure ethanol evaporation rates in covered and uncovered glasses filled with wine, in order to determine if it can have an effect on the sensory properties of wines.
Project layout
Trial 1: 2014 Cabernet Sauvignon wine (50 ml) was poured into standard XL5 wine glasses. One set was covered immediately, one set left uncovered with no direct airflow and one set uncovered with direct airflow from the laboratory’s air conditioner. Ethanol and density of the wines were measured at specific time intervals.
Trial 2: Two white wines, two red wines and two fortified wines were subjected to the same conditions as in trial 1. Ethanol concentration was measured before and after two hours.
Trial 3: the same wine from trial one was poured in three differently shaped glasses (50ml): XL5, sparkling wine and Riedel. A 100 ml XL5 was also included in the trial. Ethanol concentration was measured before and after two hours.
Sensory analysis was performed on wines with 18 judges. GC/MS analysis was also performed to determine changes in fermentation volatiles.
Results
Trial 1: There was no significant change in the alcohol content of the covered wine over the six hour time period. The uncovered wine had a gradual loss of 1% alcohol and the uncovered wine exposed to airflow had a 3.2% loss in alcohol concentration. Sensory analysis was performed after two hours with covered and uncovered (exposed to air flow) wines. 13 of the 18 judges could correctly identify the different wine indicating evaporation had a significant effect on wine sensory properties.
Trial 2: Covered wines showed no change in alcohol concentration after two hours but uncovered wines showed a loss of 0.2 – 1.9% depending on the airflow. GC/MS analysis revealed 11 of the 15 volatiles measured to be significantly lower in concentration than in the covered wine.
Trial 3: There was no change in the ethanol concentration in the different covered glasses. In the uncovered glasses not exposed to airflow the XL5 (100 ml) and sparkling wine glasses had a 0.1% reduction in ethanol concentration after two hours, the XL5 (50 ml) had a 0.2% reduction and the Riedel glass a 0.6% reduction. In the exposed to airflow wines the XL5 (100 ml) wine had a 0.7% loss, XL5 (50 ml) a 1% loss, the sparkling wine glass a 1.1% loss and the Riedel glass a significant 1.8% loss.
Significance of the study
The ethanol concentration of wine in uncovered glasses decreased significantly over time, with ethanol concentration in glasses exposed to direct airflow decreasing more rapidly. Ethanol decrease was correlated to a decrease in some volatile aromas. Due to the nature of how wine is consumed by consumers the effect of ethanol evaporation is negligible. However in the case of wine shows where poured wine is not covered, timing from pouring to judging is crucial. Small changes in ethanol concentration can influence a wine’s sensory attributes as have been demonstrated with many alcohol “sweet spot” experiments.
Reference
David Wollan, Duc-Truc Pham, and Kerry Leigh Wilkinson. Changes in Wine Ethanol Content Due to Evaporation from Wine Glasses and Implications for Sensory Analysis. Journal of Agricultural and Food Chemistry 2016 64 (40), 7569-7575. DOI: 10.1021/acs.jafc.6b02691
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