TY - JOUR T1 - Fe(II):Fe(III) Ratio and Redox Status of White Wines JF - American Journal of Enology and Viticulture JO - Am. J. Enol. Vitic. DO - 10.5344/ajev.2015.15088 SP - ajev.2015.15088 AU - John C. Danilewicz Y1 - 2016/01/05 UR - http://www.ajevonline.org/content/early/2015/12/23/ajev.2015.15088.abstract N2 - Iron plays a key role in wine oxidation. Polyphenols containing catechol systems are the main reductants and it is proposed that the oxidation of these substances is mediated by the redox cycling of the Fe(III)/Fe(II) couple. At any time the Fe(II):Fe(III) concentration ratio should depend on the rate of Fe(II) oxidation by oxygen relative to that of Fe(III) reduction by polyphenols. Fe(III) oxidation of polyphenols, though facilitated by sulfite, is somewhat slower than the reaction of Fe(II) with oxygen, which is much accelerated by Cu. Alongside this process Fe(III) inhibits is own formation. Therefore, the Fe(II):Fe(III) concentration ratio is determined by the interplay of a number of competing reactions. However, because of the relative speed of Fe(II) oxidation, oxygen should be a major determinant of this ratio. A simple spectroscopic method using Ferrozine is used to measure Fe(II) concentration in wines collected under nitrogen with minimal disturbance so as to determine its concentration in its original container. However, Fe(III), which becomes a strong oxidant in the presence of Ferrozine, oxidizes catechols in wine conditions. Therefore, Fe(II) concentration, which increases, was followed over time and extrapolated back to the moment of Ferrozine addition. Total Fe concentration was determined by adding ascorbic acid to reduce the Fe(III). As expected the Fe(II): Fe(III) ratio was higher in bottles with screw caps than a natural cork or from wine boxes. Exposure of wines to oxygen lowers the ratio, which on aerial saturation reaches equilibrium after some days. However, the ratio attained differed in different wines, which should be dependent on constituents that alter the relative rate of Fe(II) oxidation and of Fe(III) reduction. ER -