
Reaction Mechanisms of Copper and Iron with Hydrogen Sulfide and Thiols in Model Wine
Abstract
Fermentation derived sulfidic off-odors due to hydrogen sulfide (H2S) and low molecular weight thiols are commonly encountered in wine production and removed by Cu(II) fining. However, the mechanism underlying Cu(II) fining remains poorly understood, and generally results in increased Cu concentration that lead to deleterious reactions in finished wine. The present study describes a mechanistic investigation of the iron and copper mediated reaction of H2S, cysteine, 3-sulfanylhexan-1-ol, and 6-sulfanylhexan-1-ol with oxygen. The concentrations of H2S, thiols, oxygen, and acetaldehyde were monitored over time. It was found that Cu(II) was rapidly reduced by both H2S and thiols to Cu(I). The addition of Fe(III) in combination with Cu resulted in the rapid reduction of Fe(III) by Cu(I) and the resulting Fe(II) redox cycled by reacting with oxygen. Furthermore, the presence of Fe and thiols prevented the removal of H2S by precipitation as insoluble CuS promoting H2S oxidation and formation of polysulfides, effectively keeping both metals and sulfide species in wine after the copper fining process.
Issue: Macrowine 2016
Type: Article
Authors
*Penn State University