Evaluation of putative precursors of key 'reductive' compounds in wines post-bottling

Precursors to hydrogen sulfide (H₂S), methanethiol (MeSH), ethanethiol (EtSH), and dimethyl sulfide (DMS) were assessed in wines post-bottling, and the percent yield of VSCs from each precursor determined. Cysteine (Cys) and glutathione (GSH) were associated with small increases in H₂S concentrations, with a maximum yield of 0.18% and 1.3%, respectively. Greater yields of H₂S were obtained from the combined Cys/GSH and copper treatments in white wine. Copper, acting on unknown precursors, was associated with large increases in H₂S in Shiraz wines. Dimethyl disulfide and methyl thioacetate were important precursors to MeSH, and produced maximum yields of 72% and 33%, respectively. Ethyl thioacetate was a key precursor to EtSH, with a maximum yield of 39% obtained. Copper and pH were important in modulating MeSH and EtSH accumulation in wines. A maximum yield of 23% of DMS from S-methylmethionine was obtained, with dimethyl sulfoxide producing significantly less DMS with a maximum yield of only 9.4%.