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.
Dosage varies when used to kill wild bacteria in must, halt fermentation, or preserve finished wines against oxidation. The addition of ¼ teaspoon of sodium metabisulfite to 5 gallons contributes approximately 50 ppm of free SO2.
To make a sanitizing rinse for equipment, dissolve 8 teaspoons of sodium metabisulfite into 1 gallon of water. High concentrations of sulfur dioxide gas are irritating and toxic, so use in a well ventilated area. After applying the solution to your equipment, the items must be rinsed with clean, cold water.