Factors affecting flavonols instability of red wines due to climate change

Abstract

Due to varietal factors, the formation of undesirable deposits of flavonols, especially quercetin (Q), occurs in several red wines. In recent years, this phenomenon has been aggravated by excessive exposure of grapes to UV radiation during the ripening process. This is an important issue that is difficult to address, especially since it is almost impossible to define the solubility of Q in red wine, given the complexity of the matrix and the Q crystallization process in wine solution. With the aim of understanding the factors affecting the solubility of Q in red wines, a first experiment was carried out in model solution and the data showed that the solubility of Q increased by increasing the concentration of anthocyanins, but the effect depended on the time. To understand if the data obtained in model solution were confirmed in real wines, in a second experiment the changes in flavonol composition of 32 red wines from 15 different grape varieties, obtained from the same vintage and not aged in contact with wood, were evaluated. The wines were selected to show the greatest differences in composition in terms of basic and phenolic parameters. The data showed that the most important factors influencing the formation of instability were not only anthocyanins, but also tannins, which improved the solubility of Q (p<0.05), and pH (p<0.05), which instead increased the formation of deposits containing Q in real wines after 8 months of aging under controlled conditions. These results may help to better determine the risk of Q instability in red wines and possible oenological strategies to counteract it.