Copper(II) addition to white wines containing hydrogen sulfide: residual copper concentration and activity

Abstract

Background and Aims The long-term effectiveness of copper(II) to remove sulfidic off-odours remains the subject of debate. This study was undertaken to assess the extent of copper removal after its addition to white wine that contained a variable concentration of hydrogen sulfide and to investigate the activity of the residual copper in a reaction relevant to white wine ageing. Methods and Results After the addition of sulfide to white wine, copper(II) was added to give an increasing mole ratio of hydrogen sulfide to copper(II). After settling for 1–5 days, negligible copper was removed after racking or filtering (0.45 or 0.20 μm), as determined by flame atomic absorption spectroscopy. Model wines were used in an attempt to ascertain the wine components that may interfere with the removal of the copper sulfide precipitate. Residual copper in the white wine after racking was active in mediating the production of a phenolic pigment. Conclusions Copper sulfide is not easily removed from white wine once formed. Model studies confirmed that tartaric acid is a critical factor influencing the extent of copper sulfide precipitation. Significance of the Study This study demonstrates that after addition of copper(II) to wines containing sulfide, the presence of residual copper is unavoidable and remains active in mediating reactions.