A white-yellow powder, Potassium Metabisulfite (K2S2O5) is a common means of adding sulfite to wine. Potassium Metabisulfite is 57% sulfur dioxide which, when not bound to other substances in wine, acts as a preservative. In high dosages, sulfites have the taste and odor of burnt matches, in low doses, they are essentially undetectable. Approximately one in 10,000 people are allergic to sulfites.
Also see Campden Tablet and Sodium Metabisulfite. One of two sterilizing compounds which may be contained in Campden tablets, the other being sodium metabisulfite. Its action, in water, inhibits harmful bacteria through the release of sulfur dioxide, a powerful antiseptic. It can be used for sterilizing equipment and the must from which wine is to be made. Being twice as strong as sodium metabisulfite, it is mixed at half the strength of the other. For equipment, a 1/2% solution (1/2 oz. dissolved in 1 gallon of water) is sufficient after washing. After rinsing with the solution, the equipment should not again be rinsed. For sterilizing the must, a 5% solution is made (2 oz. dissolved in 1 quart of water) and from this 1 tsp. is added to the must. Wait 24 hours after sterilizing the must before adding the yeast. Both bottles of solution (1/2% and 5%) should be clearly labeled as to strength and active compound to prevent disastrous mistakes, and both may be stored in a cool place for up to one year without effecting potency.