Potassium Metabisulfite effectively kills wild yeast and bacteria. The condition of your grapes and pH levels may vary the amount needed. This agent helps your yeast do its job. Sulfites also aid in inhibiting enzymatic browning in white wines, and improves the flavor when used correctly. Use 2 oz. per 1 gallon of water. A use 1/4 teaspoon to 5 gallons of Must. Dissolve sulphite in warm water before adding.