Effects of Low-Level Oxygenation in Winemaking on Wine Phenolic Constituents.

The influence of different regimes of low-level oxygenation in winemaking and the combination oxygen/oak staves on phenolic composition in two commercial-scale trials was investigated (season 2002-2003). For the first trial, Syrah wine was treated with low, medium, and high levels of oxygen additions (for a period of two months). The analysis of phenolic concentration and composition was followed up on a weekly and monthly basis (depending on the stage of the treatments), through both chromatographic and spectral methods including normal phase-HPLC, reversed phase-HPLC, Folin-Ciocalteu, co-pigmentation assay, and a protein precipitation assay for tannins and polymeric pigments. Only small differences in the formation of polymeric color were detected for this trial. For the second experiment, Cabernet Sauvignon wine in post-malolactic fermentation, with and without oak staves, was treated with oxygen at a continuous rate of 5 mL of oxygen/L of wine/month for 6 months. Oxygen flow levels and dissolved oxygen (DO) concentrations were measured with sensitive devices at ppb levels. To allow wine sampling and determinations of DO while minimizing air-oxygen contamination, a sample circulation system was built using stainless steel tubing. Differences of up to 5 times in the concentration of dissolved oxygen were found when comparing the oxygen treated wines versus the control wines, the total acetaldehyde concentration (Gas chromatography, FID) was also significantly higher, with values 8 to 15% higher for the oxygenated treatments. Regarding the concentration and composition of phenolics (determined using the same analytical tools already described for the first experience) it was determined that the total levels of phenolics were not significantly different (~2,400 mg/L equivalents of gallic acid), however, a trend for higher concentration of small polymeric pigments, lower concentration of quercetin and gallic acid, and increases in the fraction of color due to polymeric pigments were found, among others. Future research should include the evaluation of free radical levels and the sensory effects of such treatments.