Potassium metabisulfite, or SO2 as it is often called, is used to prepare wine musts and other fruit juices for fermentation as well as to prevent oxidation in finished wines and ciders. When added to wine it generates sulfur dioxide which protects both the color and delicate flavors of the wine. The most common form of mebisulfite used in wine is potassium metabisulfite. Dosage is pH dependent but is often 50 ppm, 1/4 tsp will add 50 ppm to 6 gallons of must or wine. To use, dissolve in a small amount of wine or water and stir gently into your carboy or tank. Since potassium metabisulfite does not add sodium to the diet, it generally preferred over sodium metabisulfite.