Sodium hydrosulfite (sodium bisulfite, sodium hydrogen sulphite, sodium dithionite, E222) is an antioxidant and preservative. Chemical formula NaHSO3. In its pure form, it is a white powder with a grayish tinge.
Sodium hydrosulfite is used in light, chemical and other industries. In the food industry, it is used as a preservative or antioxidant.
Sodium hydrosulfite is used in almost all wines sold, to prevent oxidation and preserve the taste. When preserving fruit, it is used to prevent darkening and to fight germs.
In very high concentrations, it can cause serious allergic reactions.