Potassium hydrogen sulphite or potassium bisulphite
is a chemical compound with the chemical formula KHSO3. It is
used during the production of alcoholic beverages as a sterilising
agent. This additive is classified as E number E228 under the
current EU approved food additive.
It is made by the reaction of sulphur dioxide and potassium
carbonate. The sulphur dioxide is passed through a solution
of the potassium carbonate until no more carbon dioxide is given
off. The solution is concentrated and then allowed to crystallise.