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Electrochemical Microoxidation of Red Wine

¹ Graduate student (present address: Craggy Range Vineyards Limited, 253 Waimarama Road, PO Box 8749, Havelock North, Hawkes Bay, New Zealand)² Graduate student (present address: Pernod Ricard, Corbans Winery, 91 Thames St, Pandora, PO Box 7095, Napier, New Zealand)³ Lecturer, and ⁴ Director Wine Science, The University of Auckland, Private Bag 92019, Auckland, New Zealand.

^* Corresponding author (email: p.kilmartin{at}auckland.ac.nz)

A new approach to red wine aging was examined that uses a current passed continuously through glassy carbon electrodes in a process of electrochemical microoxidation. A Cabernet Sauvignon wine in 300-L tanks was subject to treatments run in triplicate over 12 weeks at 16°C consisting of a control, oxygenation to 0.67 mg/L twice weekly (equivalent to 4 mL O₂ per liter wine per month), and electrochemical oxidation of 6144 µA using 250 x 6-mm glassy carbon rods. The potential at the electrode was observed to exceed 2 V, where both oxidation of wine polyphenols and direct oxidation of ethanol can occur. While there was considerable loss of bound SO₂ in the oxygenated wines, the concentration of bound SO₂ in the electrochemical microoxidation wines actually increased as the trial proceeded, consistent with the rise in acetaldehyde observed in these wines during the final weeks of the trial. There was little change in concentrations of individual polyphenols, although the rate of decline in monomeric anthocyanins and free quercetin was greater in the oxygenated and electrochemical microoxidated wines than in the controls. Spectrophotometric measures showed an increase in SO₂-resistant pigments and a larger modified hue value (420/520 nm) in both oxygenated and electrochemical microoxidated wines. Electrochemical microoxidation provides an alternative technology for aging red wines with precise control of the rate of oxidation and treatment cut-off.

Key words: microoxygenation, polyphenols, electrochemistry, glassy carbon