Accurate measurements of the major active sulfur dioxide species in wine (HSO3- and SO2) are important for understanding wine oxidation chemistry and microbial stability. These so-called 'Free SO2' forms are classically measured by either iodometric titration or by aspiration-oxidation, both which require sample dilution and/or pH shifts, resulting in partial hydrolysis of covalently bound HSO3- adducts and overestimation of free SO2 species. We describe a simple headspace method utilizing colorimetric gas detection tubes for quantifying molecular SO2 in wine. The method requires no dilution or acidification steps and is appropriate for both research and winemaking settings. Henry's coefficients were constant over ethanol concentrations of 0-17% v/v, indicating the appropriateness of the method for table wines. Good agreement among methods was achieved for white wines, but molecular SO2 in red wines was nearly 3-fold lower using the new method, likely because classic methods measure weakly bound bisulfite-flavylium adducts.

Gas detection tubes for headspace sulfur dioxide measurements of wines

248th National Meeting (2014)

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