Formation of hydrogen sulfide in wine: Interactions between copper and sulfur dioxide

Abstract

The combined synergistic effects of copper (Cu2+ ) and sulfur dioxide (SO2 ) on the formation of hydrogen sulfide (H2 S) in Verdelho and Shiraz wine samples post-bottling was studied over a 12-month period. The combined treatment of Cu2+ and SO2 significantly increased H2 S formation in Verdelho wines samples that were not previously treated with either Cu2+ or SO2 . The formation of H2 S produced through Cu2+ mediated reactions was likely either: (a) directly through the interaction of SO2 with either Cu2+ or H2 S; 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 H2 S 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 H2 S post-bottling was demonstrated. When present in equimolar concentrations a 1:1 ratio of H2 S- 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 H2 S and SO2 , with wine matrix compounds play a critical role in modulating final H2 S concentrations in wines.