White wines oxidation-reduction potential

Copper is in an oxidized state, divalent Cu +, in aerated wines. However, when white wines are kept in the absence of air and the oxidation-reduction potential reaches a sufficiently low level, the copper is reduced to Cu+ in the presence of sulfur dioxide. This is likely to cause turbidity at concentrations of around 1 mg/1. Unlike ferric casse, copper casse develops after a long period of aging in the absence of air, at high temperatures and in bright light. It may disappear in contact with air. 

The oxidation-reduction potential of white wine decreases on exposure to natural light. This property is used to reduce copper and assess the risk of copper casse (Section 4.7.3). In the past, there was even a method of preventing copper... 

Fig. 13.5. Example showing changes in the oxidation-reduction potential of a white wine during winemaking with stirring of the lees AF, alcoholic fermentation (Vivas and Glories, 1995)...

It has been observed that the bonqnet of red and white wines develops after only a short period of bottle aging, generally when all the dissolved oxygen has reacted and the oxidation-reduction potential has reached its lowest value (<200 mV). This varies with the type of wine, its SO2 concentration and the type of closure (cork, etc.). High temperatures and light stimulate reduction in the medinm and modification of the aromatic characteristics. 

Fig. 9.4. Evolution of oxidation-reduction potential of reduced wines, aerated after the addition of 100 mg of ascorbic acid per liter, compared with control wine (Rib6reau-Gayon et ah, 1977). (A) Red wine control. (B) Red wine + ascorbic acid. C) White wine control. (D) White wine + ascorbic acid...

In certain cases, ascorbic acid improves the taste of bottled wines. Wines generally taste worse when they contain dissolved oxygen and have an elevated oxidation-reduction potential. Ascorbic acid permits a better conservation of wine freshness and fruitiness—especially in certain types of dry or sparkling white wines. It also decreases the critical phase that follows botthng, known as bottle sickness . The effect is not as considerable or spectacular for aU wines but wine quality is never lowered by its use. 

Fig. 13.17. Influence of the aging method on the oxidation-reduction potential of white wine (Dubonrdieu, 1992)...

Independently of its disinfectant properties, sulfur dioxide is widely used to protect wines from oxidation (Volume 1, Section 8.7.2). It thus contributes to the oxidation-reduction buffer capacity and prevents an increase in potential that would otherwise occur when oxygen is dissolved. Due to their structure, white wines require a higher dose of SO2 than red wines to ensure effective protection. 

The effect of the nonalcoholic components of red wine was also studied [101,102]. By using wine and alcohol-free red wine extract, it was shown that although the alcohol component of the wine may be important for a favorable lipid pattern, such potential health benefits may be independent of the proposed antioxidant effects of red wine [92,100,103,104], In a 2001 study it was shown that polyphenols in dealcoholized red wine can reduce in vivo lipid peroxidation, as measured by F2-isoprostanes, in smoking subjects, whereas no reduction in lipid peroxidation was observed after red or white wine consumption [102], In 2001 human intervention study [102], it was shown that alcohol-free red wine extract can inhibit LDL oxidation ex vivo. A short-term ingestion of purple grape juice reduced LDL susceptibility to oxidation in patients with coronary artery disease [105,106]. 

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