Sodium Sulphite
What it does
Preservative/antioxidant.
How it's made
Synthesised sulphite salt.
Sodium sulphite is a sulphite preservative and antioxidant used to prevent oxidation, browning and microbial spoilage in various foods, and as a source of sulphur dioxide. It is one of the family of sulphite salts derived from sulphur dioxide.
It is made by reacting sulphur dioxide gas (from burning sulphur) with a sodium base such as sodium hydroxide or sodium carbonate in solution. Controlling the amounts gives sodium sulphite, which is then crystallised out of the solution.
The crystals are dried to a white powder. In food it acts by releasing sulphur dioxide, which does the antioxidant and preservative work, and it must be declared on labels as a sulphite because of the sensitivity some people, especially asthmatics, have to these compounds.
Possible reactions
Sulphite-sensitive and asthmatic people may react.