Increase in the oxygen stable isotopic composition of water in wine with low ethanol yield.

The stable isotopic composition of oxygen (δO) in wine is often analysed to determine the geographic origin of the wine and the amount of water dilution. However, little is known regarding the effects of two major winemaking techniques (the addition of acid (acidification) and sugar (chaptalization)) on the δO value of water in wine. Here we show that acidification and chaptalization have minor direct effects on the δO value but indirect effects based on the ethanol yield, which causes isotopic variation of up to 0.6‰. During fermentation, δO values increase at low ethanol yields, suggesting that yeast release water with a high δO value into wine when consuming sugars. Additionally, the ethanol yield is negatively correlated with the consumption of amino acids by the yeast, indicating that yeast growth decreases the ethanol yield. We therefore identify ethanol yield, which is decreased by the consumption of sugars by yeast for non-alcohol-fermentation processes as a potential factor leading to variations in the δO value of water during the winemaking process.