Ingrid Weilack,* Sandra Feifel, Pascal Wegmann-Herr, Dominik Durner, and Fabian Weber
*Rheinische Friedrich-Wilhelms-Universität Bonn, Friedrich-Hirzebruch-Allee 7, 53115 Bonn, Germany (weilack@uni-bonn.de)

Tannins are arguably the most important group of polyphenols for red wine quality, as they are responsible for mouthfeel and color stability. During red wine aging, tannins incorporate anthocyanins and form protein-precipitable polymeric pigments, ensuring the longevity of wine color. The formation of polymeric pigments is determined by the concentrations of tannins and anthocyanins, which in turn are influenced by their extractability, grape maturity, and their ability to interact with each other. In this study, wines were made from Pinot noir and Cabernet Sauvignon grapes of three consecutive maturity stages, using different winemaking techniques including varying numbers of punch-downs and the increase of the potential alcohol content. Red wine polyphenols were characterized by their polarity using normal-phase chromatogra­phy, protein precipitation assay, and color. Additionally, wine sensory analysis was conducted. Anthocyanin concentrations in the wines increased according to grape ripeness and were minimally affected by changes in the winemaking protocol. While tannin concentration was increased significantly in the early-harvest variants with higher alcohol levels, the proportion of pigmented tannins remained unchanged. However, the fraction of polar polymeric pigments increased, along with a harder mouthfeel and a coarse astringency of the wines. This shows that the formation of protein-precipitable polymeric pigments in red wines depends on the ratio of tannin and anthocyanin concentrations and that an excess of extracted tannins leads to an imbalanced tannin profile. Due to the altered physicochemical properties of the pigmented tannins, their interactions with proteins and polysaccharides change. This results in a change in perceived astringency, showing their importance not only for color stability but also for red wine astringency.

Funding Support: This research project was financially supported by the German Ministry of Economics and Technology (via AiF) and the FEI (Forschungskreis der Ernährungsindustrie e.V., Bonn); Project AiF 20024N.