Formation of Hydrogen Sulfide in Wine: Interactions between Copper and Sulfur Dioxide

The combined synergistic effects of copper (Cu2+) and sulfur dioxide (SO2) on the formation of hydrogen sulfide (H2S) in Verdelho and Shiraz wine samples post-bottling was studied over a 12-month period. The combined treatment of Cu2+ and SO2 significantly increased H2S formation in Verdelho wines samples that were not previously treated with either Cu2+ or SO2. The formation of H2S produced through Cu2+ mediated reactions was likely either: (a) directly through the interaction of SO2 with either Cu2+ or H2S; or (b) indirectly through the interaction of SO2 with other wine matrix compounds. To gain better understanding of the mechanisms responsible for the significant increases in H2S concentration in the Verdelho samples, the interaction between Cu2+ and SO2 was studied in a model wine matrix with and without the presence of a representative thiol quenching compound (4-methylbenzoquinone, 4MBQ). In these model studies, the importance of naturally occurring wine compounds and wine additives, such as quinones, SO2, and metal ions, in modulating the formation of H2S post-bottling was demonstrated. When present in equimolar concentrations a 1:1 ratio of H2S- and SO2-catechol adducts were produced. At wine relevant concentrations, however, only SO2-adducts were produced, reinforcing that the competition reactions of sulfur nucleophiles, such as H2S and SO2, with wine matrix compounds play a critical role in modulating final H2S concentrations in wines.