Submitted to: Washington Association of Wine Grape Growers Annual Meeting
Publication Type: Proceedings
Publication Acceptance Date: February 21, 2007
Publication Date: March 23, 2007
Citation: Lee, J., Tarara, J.M. 2007. Grape and wine phenolics: a refresher. Washington Association of Wine Grape Growers Annual Meeting. Available: http://www.wawgg.org/files/documents/Jungmin_Lee_Presentation.pdf. Interpretive Summary: This is a summary of our presentation given at Washington Association of Wine Grape Growers 2007 annual meeting, during the enology session (session title: Phenolics from Grape to Barrel). It was an introduction to, and a brief overview of, the phenolics found in grapes and wine.
Technical Abstract: Phenolics are plant secondary metabolites, and are a very diverse group of compounds. These compounds have been linked to several functions: protection from UV radiation, pigmentation, anti-fungal properties, nodule production, and attraction of pollinators and seed dispersers. The phenolic content of wine is influenced by many factors, including grape cultivar, environment, vineyard management practices, and vinification practices. Phenolics make up only 1-5% of the compounds found in wine, but are important due to their contribution towards appearance, taste, mouthfeel, and potential health benefits. Grape and wine phenolics can be divided into two groups: nonflavonoids and flavonoids. Nonflavonoids have C1C6 or C3C6 structures, and those found in grapes are hydroxycinnamic acids, hydroxybenzoic acids, and stilbenes (resveratrol). Resveratrol gets the most attention in the popular press, as the health benefits of phenolics are a hot topic, though the effect of these compounds in humans are still being sorted out by researchers. Other nonflavonoids found in wine are from oak sources (=oak tannins=hydrolyzable tannins). They are derivatives of ellagic acid (=ellagitannin) and gallic acid (=gallotannin). Flavonoids have the distinct C6C3C6 (3-ring) structure. There are three main classes in flavonoids: flavanols (= building blocks of grapes tannins), anthocyanins, and flavonols. Grape tannins (=polymers of flavanols=proanthocyanidins) are the major contributors towards making wine complex in taste. Flavanol monomers and oligomers contribute towards bitterness and their polymers contribute astringency in wine. Anthocyanins give grapes their red/ purple/ black color. Flavonols are important cofactors for color enhancements and act as a natural sunscreen in the grape berry. In summary, phenolics in grapes and wines are diverse, with widely varying concentrations and composition in wine.