Potassium bisulfite

Potassium bisulfite (or potassium hydrogen sulfite) is a chemical mixture with the approximately correctly mentioned formula chemical formula KHSO3. Potassium bisulfite in fact is not a real compound, but a mixture of salts that dissolve in water to give solutions composed of potassium ions and bisulfite ions. It is a white solid with an odor of sulfur dioxide. Attempts to crystallize potassium bisulfite yield potassium metabisulfite, K2S2O5.

Potassium bisulfite is used as a sterilising agent in the production of alcoholic beverages. This additive is classified as E number E228 under the current EU-approved food additive legislation.

Production
It is made by the reaction of sulfur dioxide and potassium carbonate. The sulfur dioxide is passed through a solution of the potassium carbonate until no more carbon dioxide is evolved. The solution is concentrated.