The effect of stopping alcoholic fermentation on the variability of H, C and O stable isotope ratios of ethanol

Stopping fermentation using chemical or physical agents is an oenological procedure carried out in order to leave a pleasant amount of residual sugar in the wine. This process is typically used in the production of some Italian sweet wines (such as the famous Moscato d’Asti), where alcoholic fermentation is stopped once the alcoholic content reaches 4.5–10%. In this study, we investigated the effect of stopping fermentation on the isotopic values of (D/H)I, (D/H)II, δ13C and δ18O of ethanol obtained from wine. We examined 126 samples obtained by partially fermenting five different must samples (N = 4 fresh musts, N = 1 desulphited must) and 18 commercial Italian sweet wines. Fermentation stage was positively correlated with the δ13C and, in particular, the (D/H)II values of ethanol, but not with the (D/H)I and δ18O values. Partially fermented musts and traditional sweet wines were characterized by lower δ13C and (D/H)II isotopic values. The (D/H)II values were outside the normal range of variability for natural wines, which means that particular care must be taken in assessing the (D/H)II of sweet wines in order to avoid misinterpreting the results.