Copper-Complexed Hydrogen Sulfide in Wine: Measurement by Gas Detection Tubes and Comparison of Release Approaches

Abstract

Recent work suggests that copper complexes may serve as a latent source of free hydrogen sulfide (H₂S) and other malodorous volatile thiols during wine storage. However, measurements of these complexes require analytical tools that are unavailable to most wineries. To facilitate additional studies of these compounds, we developed an inexpensive and convenient method for detecting copper-complexed H₂S in wine with commercially available colorimetric gas detection tubes. Using brine dilution as a pretreatment, we observed that this approach showed acceptable detection limits (0.34 μg/L) and excellent H₂S recovery from both model and real wines. Alternative approaches to H₂S release from copper sulfide complexes were also investigated, including ethylenediaminetetraacetic acid (EDTA), neocuproine, ascorbic acid, and tris(2-carboxyethyl)phosphine (TCEP), alone and in combination. EDTA resulted in loss of free H₂S. Partial recovery (35 to 70%) of H₂S from model wines was achieved with the other reagents, with the release induced by ascorbic acid being of particular interest to winemakers. In a survey of seven commercial wines, the fraction of complexed H₂S released by the brine was 80 to 95% of the total H₂S pool, with lower releases observed for neocuproine and ascorbic acid. However, in several wines, TCEP treatment released higher concentrations of H₂S from unknown precursors.