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Red wine oxidation
- See Wine Oxidation also.
- The main oxidisable compounds in red wine are phenolics, which include the red wine pigments.
- Because a high concentration of phenolics are extracted from the skins, during red wine production, red wines have a high reservoir of oxidisable compounds and hence appear less sensitive to oxidative spoilage.
- A proportion of sulphur dioxide added to red wine will loosely bind to a proportion of extracted red wine pigments, decolourising the pigment molecules and rendering that portion of SO2 ineffective.
- To inhibit microbial growth and activity in red wines the level of molecular SO2 required is 0.8 ppm. (see table or equation
- Because of SO2's binding action of colour compounds in red wine and red wine's lower pH values , the levels of FSO2 required to achieve the required level of molecular SO2 would leave the wine unacceptable decolourised.
- The SO2 bound to red wine pigments are aspirated across during the analysis of FSO2, giving a false high FSO2 values.
Hence it is not possible to accurately determine the FSO2 in red wines.
Instead recommended SO2 levels for red wine are given as 50-150 ppm of TSO2 depending on circumstances and the pH of the wine.
- Because adequate FSO2 levels in red wines, to control microbial activity, are inpracticable and can not be guaranteed, most red wines are put through malolactic fermentation, giving some microbiological stability to the wine.
- Red wine pigments become incorporated into larger compounds as time goes by and become less able to bind sulphur dioxide. Therefore sulphur dioxide additions to red wine become more effective as time goes by.
- The use of ascorbic acid in red wine can result in extensive oxidation.
- No sulphur dioxide should be added to red wine if it is to go through malolactic fermentation. (see wine, SO2 and MLF)
- If red grapes are infected with botrytis (cinerea) the oxidative enzyme, laccase can persist through to the wine and rapidly catalyse the oxidation of red wine phenolics in particular the red colour pigments in red wine.