What Is Sodium Metabisulfite?

Sodium metabisulfite is used as a food preservative, a medical antioxidant and a disinfectant for brewing and winemaking equipment. It prevents bacterial growth on equipment and in fermented alcoholic beverages, and it extends the shelf life of local anesthetics and injectable hormones by preventing them from oxidizing.

For winemaking and brewing, sodium metabisulfite is sold as Campden tablets. These tablets kill bacteria and wild yeast that grow in the process of making wine, cider and beer. They also eliminate chlorine from water, allowing chemically treated municipal water to be used for brewing.

Sodium metabisulfite has no adverse effects at ordinary food doses in people who are not allergic to its component chemicals. Individuals who are allergic to sulfites should avoid sodium metabisulfite due to the possibility of a reaction. Exposure to large amounts of sodium metabisulfite, such as in an industrial setting, may cause minor skin irritation or digestive upset.

When combined with water, sodium metabisulfite forms sulfur dioxide, an unpleasant-smelling gas that to which some individuals have an adverse reaction. Because of this, sodium metabisulfite has been replaced in some disinfectant applications by hydrogen peroxide. Sodium metabisulfite also forms sulfur dioxide when combined with strong acids or heated to high temperatures.