The effect of microoxygenation on the composition of a red wine was investigated, where oxygen was applied at both low and high rates (5 and 20 mg/L/month) through a diffuser or via permeation through polyethylene tanks. A control with no oxygen was also included. Each treatment was performed in triplicate, using a commercially made Cabernet Sauvignon wine, in nine 300-L stainless-steel and three 300-L polyethylene tanks at 16°C over 16 weeks. Spontaneous malolactic fermentation occurred simultaneously with the microoxygenation treatments. The results indicated that microoxygenation enhanced the wine color development, in which effects on pigments resistant to SO2 were more marked in the first half of the trial and more obvious influences on color density were seen during the second half of the trial. Microoxygenation, as applied in this study, did not show any effect on the desirable varietal thiol 3-mercaptohexanol, yet led to some decreases in the concentrations of undesirable off-odors, including a lowering in the concentration of methanethiol without an increase in the concentration of dimethyl disulfide. Changes in the concentrations of other reductive sulfur compounds, except the thioesters, were also affected by oxygen and further by the influence of spontaneous malolactic fermentation, indicating the complicated interactions of these compounds in the wine matrix.
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