Analysis of Free Hydrogen Sulfide in Wines Using Gas Detection Tubes

Summary Goals: Hydrogen sulfide (H₂S, “rotten egg” aroma) concerns winemakers due to its contribution to sulfur-like off-aromas (SLOs). However, there are a lack of inexpensive, convenient methods for quantitation of H₂S in wines at or below its reported odor threshold. The use of selective, colorimetric gas detection tubes (GDT) for measurement of H₂S during fermentation has been previously described, but this approach has not been adapted and validated for finished wines. We developed and validated protocols for rapid, inexpensive analysis of H₂S using GDTs and Aeration-Oxidation (A-O) glassware commonly available in wineries. Video demonstration of the approaches is also provided (Supplemental Video 1). Key Findings: Two approaches were validated for GDT-based quantitation of H₂S in wine. In the first approach, H₂S was sparged from the sample with N₂ gas, analogous to Monier-Williams analyses of SO₂. In the second approach, H₂S was sparged by a vacuum-generated air stream, analogous to A-O analyses of SO₂. Both approaches require <15 min/sample and achieve excellent linearity. The calibration curve for the N₂ Method was identical to the curve predicted from the manufacturer’s markings. The Aspiration Method was less sensitive, likely because of oxidative losses. However, the Aspiration Method was simpler to set up, operate, and adapt to higher concentration samples. The limits of detection were 12-13 ng H₂S for the methods, or ~0.2 μg/L using a 60 mL sample. The mean coefficients of variance (%CV) were <5% for both approaches. Using the new method, we observed that commercially purchased wines stored in aluminum cans have significantly higher H₂S than commercial wines in glass packaging. Significance: The novel methods can be used for routine H₂S analysis in wineries without the need for significant investment in new equipment. In addition to cost savings, the ability to test H₂S onsite rather than send samples to an external lab decreases the risk of H₂S losses through oxidation or volatilization. These new analytical tools can be used for benchmarking, diagnosing faulty wines, or evaluating the effects of winemaking parameters, such as yeast selection, remediation treatments, and packaging options on H₂S.