New Approaches to Tannin Characterization

The perception of astringency in wine is largely credited to condensed tannins (proanthocyanidins). Condensed tannins in grapes and other plants are polymers of flavanoid monomers, and possess innumerable structures due to variations in subunit structure/stereochemistry, and connection points. Methods to characterize tannins typically fall into one of three categories: characterization of the tannin monomers, operational characterization to measure the concentration of intact tannin, and functional characterization of astringency, for example, protein precipitation methods. Of existing analytical methods, those based on precipitation of tannins by proteins or other macromolecules have been particularly successful in modeling astringency in wine, as determined by trained sensory panels. Traditional protein-precipitation methods use an excess of protein, so that strong and moderate binding tannins are fully precipitated and consequently not well distinguished. Future advances in relating tannin chemistry to sensory properties may benefit from using novel analytical chemistry approaches, such as detailed mass spectral data on tannin composition.