Preliminary studies on acidity‐astringency interactions in model solutions and wines

Intensity of astringency in model solutions and wines varying in total acid and total phenols was evaluated by paired comparisons by 10 trained judges. Model solutions consisted of tannic (500, 1000, 2000 mg litre −1 ) and tartaric (0, 2, 4, 6 g litre −1 ) acids dissolved in aqueous solutions of ethanol (120 ml litre −1 ) and sucrose (5 g litre −1 ). Wine solutions were prepared by addition of citric acid (0, 0.5, 1, 2, 3 g litre −1 as tartaric acid) to a high phenol‐red wine (2645 mg litre −1 GAE) and a moderate phenol‐white wine (800 mg litre −1 GAE). At all three levels of tannic acid, astringency of model solutions increased significantly ( P <0.001) with tartaric acid concentration. Astringency of white wine also increased significantly ( P <0.05) with citric acid concentration. A negative linear relation was found between relative astringency and pH at a given tannin level for both model solutions and white wine. As pH was reduced, more phenolic molecules were in the phenol form thereby increasing the likelihood of hydrogen bonding between hydroxyl groups of wine tannins and ketoimide groups of mouth proteins. The preliminary hypothesis that hydrogen bonding is the main reaction involved in the formation of protein‐tannin complexes resulting in the sensation of astringency was reinforced.