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Wine and Juice Oxidation



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Wine and Juice Oxidation Patricia Ann Howe Patricia Howe Wines PO Box 10633 Napa CA 94581 pathowe patriciahowewines com Introduction The oxidative flaws of grape juices and wines are characterized by an increase in brown color and the development of the typical oxidative aromas of acetaldehyde acetic acid and ethyl acetate Loss of pigmentation and tannins through precipitation can also occur Oxidation is defined as the loss of electrons and relates to the status of the valance outer shell electrons this definition has less utility for the average winemaker than the noticeable byproducts Recent research in wine oxidation is demonstrating the importance of interrelated oxidative reactions and metallic cofactors in wine chemistry Awareness of the chemistry and microbiology of these oxidative processes allow the winemaker to understand prevent control or harness these reactions There are three main mechanisms of juice and wine oxidation enzymic chemical and microbiological Enzymic Oxidation Enzymic oxidation from grape tyrosinase or mold laccase enzymes present in the grape juice causes browning and in extreme cases aldehyde production These reactions require the presence of the enzymes the required substrates phenolic compounds oxygen and metallic cofactors Like most enzymes they are more active at warmer temperatures They are also more active at higher pHs and although the grape tyrosinases are denatured by ethanol the mold laccases have continued activity in wine These enzymic processes can be discouraged by judicious use of harvesting crushing and pressing parameters to minimize enzyme reaction rates and exposure to oxygen Other control measures rely mainly on removal of the enzyme via fining usually with bentonite reducing exposure to oxygen and judicious use of SO2 Some winemakers use juice hyperoxidation as a production method to reduce the phenolic and color compounds of their product Typically this relies on several saturations of the must or juice with oxygen



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