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

The stable isotopic composition of oxygen (δ¹⁸O) 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 δ¹⁸O value of water in wine. Here we show that acidification and chaptalization have minor direct effects on the δ¹⁸O value but indirect effects based on the ethanol yield, which causes isotopic variation of up to 0.6‰. During fermentation, δ¹⁸O values increase at low ethanol yields, suggesting that yeast release water with a high δ¹⁸O 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 δ¹⁸O value of water during the winemaking process.