Sodium Metabisulfite is a common additive used to preserve and stabilize wines, ciders, and occasionally beers. When added to wine or must, it forms sulfur dioxide gas (SO2). This prevents most wild microorganisms from growing and acts as a potent antioxidant, protecting both the color and delicate flavors of wine. Sodium metabisulfite solutions are also used as sanitizing rinses for winemaking equipment.
Sodium metabisulfite functions identically to potassium metabisulfite. Potassium metabisulfite is usually preferred as an additive becuase it does not contribute any dietary sodium, but sodium metabisulfite is more popular as a sanitizing rinse.