Effect of wine closure oxygen permeability on volatile sulfur compounds in Pinot noir and Chardonnay wines during post-bottle aging

It is generally assumed that bottled wine is a dynamic system. A proper wine bottle closure will allow a dynamic and healthy gas exchange between the wine the air. The amount of oxygen ingression through the wine closure can directly affect wine aging and flavor development. Too much oxygen ingress can oxidize the wine during post-bottle aging, whereas too little oxygen ingress may slow flavor development. It is a concern that screw caps with too low oxygen permeability may even induce ?reduced? sulfur off-flavor due to accumulation of volatile thiols. To test this hypothesis, natural cork (up and down), synthetic, and screw caps with Saran-Tin, Saranex and low density polyethylene (LDPE) lines with various oxygen permeability were investigated on both Pinot noir and Chardonnay wines over two years storage. For Chardonnay wine, the LDPE screw cap gave the highest dissolved oxygen, lowest free SO2, and highest absorbance at 420 nm. The Saran-Tin screw cap gave the lowest dissolved oxygen. Similar trends were observed for Pinot noir wines, with Saran-Tin screw cap gave the lowest dissolved O2 and highest free SO2 and total SO2. Decreasing trend was observed for some sulfur compounds during 2 years of storage. Methanethiol had the highest decrease in wines with LDPE screw cap and synthetic closures, correlated with high oxygen permeability of these closures and low SO2 content in the wines. Similar pattern was observed for H2S. On the other hand, a decreasing trend was observed for ethylthiol acetate due to hydrolysis, and was not affected by closure types. Other sulfur compounds remained stable or decreased slightly, and there was no elevated sulfur compound for any screw cap closures after two years of storage. In addition, we did not detect any significant amount of dimethyl disulfide and dimethyl trisulfide in any of the experimental wines. Expert sensory panel did not pick up sulfur off-flavor in the experimental wines, and trained sensory panelist did not pick up any aroma difference between the Saran-Tin and LDPE screw capped wines. These results suggest the original wine status was probably more important, and the data does not support the hypothesis that dimethyl disulfide could converted to methanethiol under low oxygen conditions.