Potassium Metabisulfite is a winemaking agent used primarily as an antioxidant, sterilizer, and stabilizer. It prevents most microorganisms from growing, and it protects both the color, and flavors of wine. It will lose its effectiveness over time, so a good rule of thumb is to replace your supply at least annually. Old metabisulfite can be used as sanitizer. To stabilize fermented wine, dose up to 1/4 tsp. per 6 gallons of finished product for solid protection of wine and to allow for back sweetening of wine with no additional fermentation. For use as a general sanitizing solution, dilute 2 tsp. of metabisulfite in a standard size spray bottle with water to provide a 1% solution suitable to spray all equipment used in the winemaking process, or add 2 oz per gallon of water.