Sodium pyrosulfite (metabisulfite, sodium pyrosulfite, sodium metabisulfite, E223) is a preservative, antioxidant, and disenfectant. White crystalline powder. Melting point: 150 °C. Chemical formula Na2S2O5.
It is present in many sweet bars. It is used in the production of wines and beer.
A safe daily dose of up to 0.7 mg per kilogram of body weight. It has no side effects — it is oxidized in the liver to safe sulfates and is excreted in the urine. It can cause allergic reactions in people who are sensitive to it. Upon contact with acids, it emits a toxic gas. Contact with eyes may cause eye damage.