Abstract
<h3>Summary</h3> <h3>Goals:</h3> Hydrogen sulfide (H<sub>2</sub>S, “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 H<sub>2</sub>S in wines at or below its reported odor threshold. The use of selective, colorimetric gas detection tubes (GDT) for measurement of H<sub>2</sub>S 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 H<sub>2</sub>S using GDTs and Aeration-Oxidation (A-O) glassware commonly available in wineries. Video demonstration of the approaches is also provided (Supplemental Video 1). <h3>Key Findings:</h3> Two approaches were validated for GDT-based quantitation of H<sub>2</sub>S in wine. In the first approach, H<sub>2</sub>S was sparged from the sample with N<sub>2</sub> gas, analogous to Monier-Williams analyses of SO<sub>2</sub>. In the second approach, H<sub>2</sub>S was sparged by a vacuum-generated air stream, analogous to A-O analyses of SO<sub>2</sub>. Both approaches require <15 min/sample and achieve excellent linearity. The calibration curve for the N<sub>2</sub> 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 H<sub>2</sub>S 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 H<sub>2</sub>S than commercial wines in glass packaging. <h3>Significance:</h3> The novel methods can be used for routine H<sub>2</sub>S analysis in wineries without the need for significant investment in new equipment. In addition to cost savings, the ability to test H<sub>2</sub>S onsite rather than send samples to an external lab decreases the risk of H<sub>2</sub>S 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 H<sub>2</sub>S.
Highlights
Two approaches were validated for gas detection tubes (GDT)-based quantitation of H2S in wine
H2S is reported to be in the range of 1-20 μg/L in wines at the end of fermentation[11], and its low concentration and high reactivity requires the use of specialized analytical approaches
The use of GDTs for measurement of H2S in enological studies was first reported for measurement of total H2S produced by yeast strains during small-scale fermentations[14, 15]. These reports use the CO2 produced during fermentation to force H2S through the GDT, an approach that is not viable for post-fermentation wines without CO2
Summary
Two approaches were validated for GDT-based quantitation of H2S in wine. H2S is reported to be in the range of 1-20 μg/L in wines at the end of fermentation[11], and its low concentration and high reactivity requires the use of specialized analytical approaches. A modern version of classic colorimetric approaches utilizes gas detection tubes (GDT) for selective H2S quantification.
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