Analysis of Free Hydrogen Sulfide in Wines Using Gas Detection Tubes

Abstract

Summary Goals: Hydrogen sulfide (H2S, “rotten egg” aroma) concerns winemakers due to its contribution to sulfur-like off-aromas, and convenient methods are needed for quantitation of H2S in wines at or below its reported odor threshold. The use of selective, colorimetric gas detection tubes (GDTs) 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 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, but this method was simpler to set up, operate, and adapt to samples with higher concentrations. The limits of detection were 12 to 13 ng H2S for the methods, or ~0.2 μg/L using a 60-mL sample. The mean coefficients of variance were <5% for both approaches. Using these methods, we observed that commercial wines stored in aluminum cans have significantly higher H2S content than commercial wines in glass packaging. Impact and Significance: Wineries can use these novel methods for routine H2S analysis without significant equipment investment. In addition to cost savings, the ability to test H2S onsite, rather than sending samples to an external lab, decreases 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.