The effects of copper fining on the wine content in sulfur off-odors and on their evolution during accelerated anoxic storage

Three different red wines with reductive character have been treated with two different doses of copper sulfate (0.06 and 0.5 mg/L) and with a commercial copper-containing product at the recommended dose (0.6 mg/L). Wines were in contact with copper one week, centrifuged and stored at 50 °C in strict anoxia for 2 weeks (up to 7 in one case). Brine-releasable (BR-) and free fractions of Volatile Sulfur Compounds were determined throughout the process. Relevant increases of BR-H2S suggest that those wines contained other H2S precursors non-detectable by the brine dilution method. Copper treatments had two major effects: 1) immediate decrease the levels of free H2S and methanethiol (MeSH); 2) slow the rate at which free H2S (not MeSH) increases during anoxic storage. After 7 weeks of anoxia levels of free H2S and MeSH were high and similar regardless of the copper treatment. Higher copper doses could induce the accumulation of BR-H2S