CORRELATIONS OF CARBON-ISOTOPE RATIOS OF WINE INGREDIENTS FOR THE IMPROVED DETECTION OF ADULTERATIONS .1. ORGANIC-ACIDS AND ETHANOL

The delta(13)C-values of organic acids and their correlations to those of the sugar and ethanol, respectively, from 57 EU data bank wines of the Rheinpfalz area (years 1991-1993) and from some of their correspo nding musts have been determined. In addition to the well established difference between fermented sugar and ethanol (Delta delta(13)C = -1. 7+/-0.2 parts per thousand), a new constant correlation was found in w ine for ethanol and citric acid (Delta delta(13)C = +2.4+/-0.4 parts p er thousand). From this result a fixed delta-value difference for citr ic acid in wine to the fermented sugar of +0.7+/-0.6 parts per thousan d can be deduced. The delta(13)C-values of L-malic acid and L-tartaric acid in must were not altered by the alcoholic fermentation; they sho uld therefore directly provide access to the delta(13)C-value of the n atural sugar in must. However, in non-adulterated wines the expected d elta(13)C-value differences between these acids and ethanol showed uns atisfactory correlation coefficients. For L-malate this is attributed to the secondary (partial) degradation of this acid by the malolactic fermentation; a corresponding correction is envisaged in order to make L-malate available as an internal standard. As a reason for the unsat isfactory correlation between L-tartaric acid and ethanol, it is suppo sed that the time of its maximum biosynthesis period does not coincide with that of glucose in the grape ripening period.