Sulphur Dioxide
What it does
Preservative and antioxidant.
How it's made
Produced by burning sulphur or as a by-product.
Sulphur dioxide is a versatile preservative and antioxidant used to prevent spoilage, browning and oxidation in dried fruit, wine, fruit juices, and many other products; it also inhibits bacteria and preserves colour and vitamin C. It is a pungent gas with a long history of use in winemaking.
It is produced industrially by burning sulphur in air, which combines the sulphur with oxygen to form sulphur dioxide gas; it is also recovered from the roasting of sulphide ores and from other industrial processes. The gas is then purified and can be compressed into a liquid under pressure.
For food it is used either as the gas, dissolved in solution, or generated from sulphite salts. It is a well-known allergen-style trigger for some people, particularly those with asthma, which is why sulphur dioxide and sulphites must always be declared on labels when present above a low threshold.
Possible reactions
Can trigger asthma, wheezing and headaches; a declarable allergen above 10 mg/kg.