Control of wine vinegar authenticity through δ18O analysis

Production of wine vinegar by fermenting dried grapes and rehydrating with tap water is not allowed by European Regulations. In this study we proved experimentally that δ18O analysis of beverage water, officially used to detect the watering of wine and rehydration of concentrated fruit juice, can also be applied to vinegar to detect this kind of fraud. We considered fourteen production chains from wine to the corresponding raw vinegar and diluted vinegar (6% of acidity), and the official European Wine Databank established according to EU Reg 555/2008. 18O limit values of -2‰ and -5‰ were defined for raw and diluted vinegars produced from fresh grapes. Values lower than these limits indicate a significant addition of water to a starting matrix with a sugar concentration much higher than fresh grapes. On this basis, more than 60% of 92 suspicious wine vinegars imported to the Italian market were shown not to be authentic, but rather obtained by diluting a concentrated source such as dried grapes with water.