Potassium Meta-bisulfite, or SO2 as it is often referred by, is used to help control spoilage bacteria and indigenous yeast as well as oxidation. The most common form of Meta-bisulfite is as a powder which is fixed with potassium or sodium. This versions is fixed with Potassium. 1/4 tsp adds 50 ppm to 5 gallons of must or wine. The exact amount needed to effectively protect the wine is determined by the wine's ph. Dissolve in a small amount of wine and stir gently into your vessel.