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

Abstract

Three different red wines with reductive character have been treated with two different doses of copper sulfate (0.06 and 0.5mg/L) and with a commercial copper-containing product at the recommended dose (0.6mg/L). Wines were in contact with copper one week, centrifuged and stored at 50°C in strict anoxia for 2weeks (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 7weeks 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.