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

- In some wines brine dilution (BR) method cannot detect some H2S precursors.
- Copper treatments (CT) remove immediately free forms of H2S and MeSH from wine.
- CT delay but do not impede the accumulation of H2S and MeSH during anoxic storage.
- CT do not remove BR-forms and seem to induce a larger formation of BR-forms.
- Copper content does not change with CT, implying no CuS is separated.

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.