Prediction method for determining the carbon stable isotopic composition of berry sugars in the original must of Chardonnay wines

Abstract The carbon stable isotopic composition, as indicated by the δ13C value, of wine ethanol is inherited from berry sugars, but little is known about the variation in sugar δ13C values of Japanese grapes relative to overseas grapes. This study found a large variation in sugar δ13C values of Chardonnay grapes grown in Japan (−27.2 ± 0.9‰, mean ± standard deviation, n = 33), with sugar δ13C values depending on the δ13C values and content of monosaccharides. After complete fermentation, the carbon isotope discrimination between berry sugars and wine ethanol was 1.5 ± 0.1‰. Ethanol δ13C values and carbon isotope discrimination enabled prediction of sugar δ13C values in the original must. Imported wines had higher sugar δ13C values than those of wines made from Japanese grapes, suggesting drier overseas viticulture conditions. The determination of sugar δ13C values in grape berries provides valuable information for viticulture and wine authentication.