New insights into the formation of precipitates of quercetin in Sangiovese wines

Wines produced from Sangiovese (sg) grapes, the most cultivated red grape variety in Italy and widely grown across the world, is often subjected to loss of clarity due to the formation of a deposit constituted by fine needle-shaped crystals. In this work, a qualitative study by 1H-NMR and 13C-NMR analysis of the deposit obtained by filtering cloudy sg wines showed that it was constituted by crystals of quercetin (Q). The analysis of hydro-alcoholic solutions (12% ethanol and pH 3.2.) and red wines added with increasing amounts of Q showed that, above 3 mgL−1 of Q, a deposit can be detected and, the time necessary for its formation depends on the medium. The comparison among sg and other 11 monovarietal wines showed that sg was the richest in Q and quercetin glycosides (GQ). Both Q and GQ decreased in the analyzed solutions over time and the decrease was faster for Q than for GQ. The controlled exposure to oxygen determined a decrease of Q higher than the 50% of the initial values. Data obtained in this study suggested that practices as micro-oxygenation and wood aging could help to decrease the amount of Q in sg wines.