Oxidation of Phenolics
Description of oxidation products and pathways in red and white wines. According to Singleton (1987), red wine can tolerate 30 saturations of air before developing flavors associated with oxidation. At 20°C that would be 180ml O2/L over the course of the wine’s aging. His suggested exposure for quality was 10 saturations. At 20°C that would be 60ml O2/L (84mg/L). For white wines, Singleton (1979) suggested that 10 saturations of air would start to develop oxidation flavors. Waterhouse suggests that modern wines have less capacity for oxygen than wines in this study, but does not specify.
Oxidation of Wine Phenolics: A Critical Evaluation and Hypotheses.
Oxidation reactions involving phenolics might change the chemical and sensory profile of wines. While oxidation is a long-standing problem in winemaking, a definitive understanding of its chemical mechanisms is lacking, and such an understanding could allow us to better predict and control wine aging. We briefly summarize and discuss the current knowledge on the chemistry of wine phenolic oxidation and propose, along with other researchers, a new, comprehensive scheme in which the Fenton reaction and hydroxyl radicals have an essential role. This hypothesis suggests that catalytic iron converts wine’s hydrogen peroxide into hydroxyl radical. This leads to a much stronger and less selective oxidant that could react with almost all wine components, in proportion to their concentration and with little selectivity for antioxidant properties. This reaction could produce many electrophilic oxidation products, mainly aldehydes and ketones, that could further modify the chemical composition and sensory perception of wine. While the brevity of this report precludes a full review of oxidation, our aim is to stimulate more study and debate on the mechanisms in wine oxidation chemistry.
AM.J. Enol. Vitic. 57:306-314