Screening of Italian red wines for quercetin precipitation risk index

Quercetin Q, a phenolic compound released from grape skins during red wine maceration, has been identified as a source of instability in bottled wines, particularly Sangiovese, due to its crystallisation. This phenomenon represents an economic challenge for producers and affects the clarity of wine and consumer perception. Recent studies have shown that anthocyanins, probably due to co-pigmentation, increase the solubility of Q, thereby reducing the risk of crystallisation. Based on these results, this study aimed to validate these findings in real red wines and to better understand the factors influencing the risk of Q precipitation. Thirty-two monovarietal Italian red wines from the same harvest, which differed significantly in phenolic composition, were analysed focusing on the quantification of Q-glycosides (Q-Gs) and aglycones in the wine bulk and the sediment when present at different time points. In 30 out of 32 wines, hydrolysis of Q-Gs occurred during the first year of ageing, but only in 2/3 of the wines analysed, Q remained soluble in solution. The remaining wines behaved like saturated solutions as Q was detected in insoluble precipitate: however, even after aging, no clear precipitation threshold could be determined. Partial least squares (PLS) regression showed that the most influential risk categories for Q precipitation were pH and the monomeric anthocyanin/flavanol ratio. In addition, the Pearson correlation analysis demonstrated that not only anthocyanins but also tannins help to make Q more soluble. Our results contribute to a deeper understanding of the factors influencing quercetin stability in red wines, with implications for producers seeking to mitigate precipitation risks.