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

The combined synergistic effects of copper (Cu(2+)) and sulfur dioxide (SO(2)) on the formation of hydrogen sulfide (H(2)S) in Verdelho and Shiraz wine samples post-bottling was studied over a 12-month period. The combined treatment of Cu(2+) and SO(2) significantly increased H(2)S formation in Verdelho wines samples that were not previously treated with either Cu(2+) or SO(2). The formation of H(2)S produced through Cu(2+) mediated reactions was likely either: (a) directly through the interaction of SO(2) with either Cu(2+) or H(2)S; or (b) indirectly through the interaction of SO(2) with other wine matrix compounds. To gain better understanding of the mechanisms responsible for the significant increases in H(2)S concentration in the Verdelho samples, the interaction between Cu(2+) and SO(2) 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, SO(2), and metal ions, in modulating the formation of H(2)S post-bottling was demonstrated. When present in equimolar concentrations a 1:1 ratio of H(2)S- and SO(2)-catechol adducts were produced. At wine relevant concentrations, however, only SO(2)-adducts were produced, reinforcing that the competition reactions of sulfur nucleophiles, such as H(2)S and SO(2), with wine matrix compounds play a critical role in modulating final H(2)S concentrations in wines.