Todd Jenkins, Andrew Waterhouse,* Patricia Howe, and Gavin Sacks
*University of California, Davis, 595 Hilgard Lane, Davis, CA 95616 (alwaterhouse@ucdavis.edu)

Sulfur dioxide (SO2) is perhaps the oldest and arguably the most important wine additive used in winemaking due to its antioxidant, antimicrobial, and enzyme-inhibiting properties. Conventional methods such as the Ripper titration, aeration-oxidation (A-O), and other analytical methods have been developed and employed widely for the quantitative analysis of SO2 in wine. However, it is clear that a large fraction of the free SO2 reported by these procedures is not actually available or ‘active’ for protecting wine, due to the effects of weak binding with anthocyanins and other common compounds present in the wine matrix. A recently developed method to measure molecular and ‘free’ SO2 in wine using gas detection tubes (HS-GDT) demonstrated that levels of free SO2 as determined by standard methods overestimate the free SO2 in many wines. However, the gas detection tube method has not been widely adopted due to its complexity, especially for many samples. We describe an automated analytical strategy based on static headspace gas chromatography using sulfur chemiluminescence detection technology (HS-GC-SCD) to obtain what we define as the truly ‘active’ free and molecular levels of SO2 in wine. The HS-GC-SCD method proposed requires minimal sample preparation, can be automated, and can achieve results in as little as 10 min when the pH and ethanol concentrations are known. We will present information on a direct comparison of the Ripper, A-O, HS-GDT, and HS-GC-SCD methods on a diverse set of wine samples. Aside from a relatively high upfront cost for a GC system, the instrument’s flexibility for other procedures, stability, and low operating costs per sample present opportunities for adoption by medium to large-sized operations. Additionally, direct measurement of ‘active’ SO2 may serve as a better predictor of wine aging and microbial stability and may be a useful tool for further research.

Funding Support: American Vineyard Foundation, Henry A. Jastro Graduate Research Award