The effects of pH and copper on the formation of volatile sulfur compounds in Chardonnay and Shiraz wines post-bottling

The effects of pH and Cu2+ treatment on the formation of volatile sulfur compounds (VSCs) were investigated in Chardonnay and Shiraz wine samples. Four VSCs were significantly affected by pH, with lower wine pH associated with decreased hydrogen sulfide (H2S), methanethiol, dimethyl sulfide, and carbon disulfide concentrations. The effects of pH and Cu2+ on H2S formation from known precursor compounds were subsequently studied in a model wine system. In samples treated with cysteine and glutathione lower pH produced less H2S. Nanoparticle tracking analysis was used to study the effects of variable pH concentrations in a model system containing Cu2+, tartaric acid, and H2S. Differences in Cu2+-tartrate complexes particle size and concentration were measured as a function of pH and H2S addition, suggesting the type of complexes formed may affect the binding sites of Cu2+ available to catalyse the formation of VSCs such as H2S.