Sulfites have been used for centuries to sanitize and preserve foods. They are used worldwide in the wine industry as antioxidant and antimicrobial agents. However, sulfites recently have been identified as causative agents in certain allergic reactions suffered by asthmatics. As a result, the FDA and the Bureau of Alcohol, Tobacco and Firearms have mandated that sulfites in foods and beverages, at levels of 10 ppm or higher, be identified on the label.

Although the regulations are based on the amount of total sulfite (the sum of the free and bound forms), wine makers, bottlers and others associated with the industry are primarily interested in the amount of free sulfite in the wine or must. The combination of sulfite with aldehydes or pigments which are naturally present may reduce the effectiveness of the additive.

The Titrimetric Method.  CHEMetrics' sulfite test kits are based on the "Ripper" method, which has long been used by the wine industry as a standard for rapid sulfite analysis. Sulfite is titrated with an iodide-iodate solution, using a starch end point indicator. Phosphoric acid is used to adjust the pH of the sample. Results are quantified using direct reading titration cells (Titrets). The test determines free sulfite as ppm (mg/L) SO₂.

Results from this test kit are acceptable for dry white wines although they can have an error of up to 10 ppm. The test is not recommended for use with red wines, or white wines containing ascorbic acid or tannin. These wines often give false high test results. As a rule, a test result of greater than 40 ppm free sulfite for any wine should be considered suspect and an alternative sulfite determination method should be employed.

The test is affected by the same interferences as the Ripper method. These include Botrytis, tannin pigments, and ascorbic acid.