The Effects of Low-Level Oxidation in Winemaking on Phenolic Constituents and Herbal Character.

Since 2002, we have been working a series of experiments to help us understand the effects of introducing small amounts of oxygen in red wine production. Despite the lack of scientific information on the subject, vendors of the popular micro-oxygenation technique have claimed for years the positive outcomes of their treatment in terms of tannin perception, wine color stability, and reduction of vegetal character. We have set the aim of this project to measure analytical, sensorial, and chemical changes of the effects of low-level oxygenation treatments in red wine production. To date, commercial and small-scale experiments have been and are being carried out. At the beginning, we focused our efforts towards the accurate determination of oxygen and phenols concentrations, and lately, we have included sensory studies, measurements of methoxy-pyrazines, and the evaluation of wine phenolic free radicals.

Some of the results we have accomplished so far are: (a) We have been able to determine that non-aggressive oxygenation might have only limited effects on phenolic composition and concentration (e.g. reductions in the levels of quercetin and small increments in the formation of polymeric pigment and total acetaldehyde). The trends in the decrease of concentration of some monomeric phenols (e.g gallic acid and anthocyanins) and increases in the concentration of tannin and polymeric color suggest that the rates of oxygenation and the time of the oxygen treatment are of primarily importance (both alternatives are been tested this year) (b) We have found dissolved oxygen concentration (in tanks and barrels) at levels that have not been reported before (ppb) (c) In general, the effects of the combination of oak and oxygen were not different that those obtained by the oxygen solely (d) Higher signals for phenoxyl free radicals in wine were found when this was exposed to oxygen. To summarize, significant advances have been made in the understanding of the technique, but there are still many questions to be answered.