H, C, and O Stable Isotope Ratios of Passito Wine

In this study we investigated the effect of the grape withering process occurring during the production of Italian passito wines on the variability of the (D/H)(I), (D/H)(II), delta C-13, and delta O-18 of wine ethanol and the delta O-18 of wine water. The production of PDO Erbaluce di Caluso Passito in five different cellars in Piedmont (Italy) was considered in two successive years. Moreover, samples of 17 different traditional Italian passito wines taken at different stages of maturation were taken into account. We found that the delta O-18 of must and wine water and the delta O-18 of ethanol decrease in the case of passito wines produced in northern and central Italy using postharvest drying of the grapes in dedicated ventilated or unventilated fruit drying rooms (fruttaio), during autumnwinter. For passito wines produced in southern Italy, where the main technique involves withering on the plant (en plein air), delta O-18 tends to increase. The (DH)I of wine ethanol did not change during withering, whereas the (DH)(II) and delta C-13 values changed slightly, but without any clear trend. Particular attention must be therefore paid in the evaluation of the delta O-18 data of passito wines for fraud detection.