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%.