Evolution of sulfonated tannins in red wines with ageing: A targeted metabolomic approach.

During wine ageing, tannins could react with sulfur dioxide to form sulfonated flavanols which are anticipated to alter tannin binding to proteins contributing to the reduction of astringency during ageing. Previous studies have identified or quantified monomeric and dimeric sulfonated flavanols in aged wines, but the evolution of sulfonated tannins has been lacking. Here, we quantified sulfonated tannins in three Washington state vineyards over a 20-year period, employing targeted LC-QToF analysis. Analysis of 24 wines revealed a systematic trajectory of sulfonated tannins over 20 years. Sulfonated monomers rose consistently with wine age, becoming the dominant form of sulfonated products in all samples at the 20-year mark. Concurrently, there was a decline in native tannins and sulfonated oligomers, suggesting a process of acid-catalyzed depolymerization of native tannins followed by sulfonation via reaction with sulfur dioxide. Future work is needed to understand the stability of sulfonated tannins and their impact on wine astringency.