Technical Report
 

Sun Exposure and Grape Phenolics

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https://ir.library.oregonstate.edu/concern/technical_reports/d504rm587

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  • Phenolic compounds are key quality components of wine affecting sensory characteristics, wine color, and wine stability. Phenolics are responsible for much of the mouth flavor of wines affecting astringency, bitterness, and the "length" of the flavor impression on the palate. The color in both red and white wine is due to phenolic pigments, primarily anthocyanins, and flavonols. Biochemical changes in the phenolic compounds in wines over time, are responsible for many of the flavor changes associated with wine aging. The primary source of most of the phenolic compounds in wine is grape skins. The total concentration of phenolics in skins is influenced by the environment of the grape clusters during their development. Generally the more light and sun exposure the cluster receives the higher will be the concentration of phenolics and anthocyanins. We have seen similar results in our research on grape canopies and wine quality at OSU. However, we have also seen that increases in total phenolic concentration are often accompanied by changes in the relative concentration of specific phenolic compounds. This was first apparent in changes in the ratio of total anthocyanins to total phenolics. Wines made from very exposed clusters had increases in total phenolics that were often much greater than the increases in anthocyanins. In 1991 we found that exposed grape skins had much higher concentrations of flavonols than shaded skins. The increase in flavonol concentration was much greater than increases in other phenolic compounds and could account for a change in the anthocyanin phenolic ratio. In 1992 we began more careful analysis of grape skins. The primary objectives were to describe changes in the phenolic profiles of grape skins exposed to the sun and to determine if these changes had an impact on the phenolic profiles of wines.
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