Potassium bisulphite

Potassium bisulphite is a sulphiting agent — a compound that generates sulphur dioxide (SO₂) when dissolved in acidic food environments — used as a preservative and antioxidant in wines, dried fruits, vegetable products, and other foods prone to microbial spoilage and oxidative browning. Sulphiting agents work by releasing SO₂, which inhibits enzymes responsible for browning, suppresses yeast and bacterial growth, and prevents vitamin C oxidation, thereby preserving colour, flavour, and shelf life.

JECFA established a group ADI of 0.7 mg/kg body weight per day expressed as SO₂ equivalents in 1967, applying to all sulphite additives (E220–E228) collectively. This conservative limit reflects the potential for adverse reactions in sensitive individuals: sulphites are significant allergens that can provoke asthma attacks, urticaria, and anaphylactic reactions in sulphite-sensitive people, a condition estimated to affect a small but significant proportion of the general population and a higher percentage of asthmatics. For this reason, EU and most global food regulations require mandatory declaration of sulphites on ingredient labels when present above 10 mg/kg SO₂.

Potassium bisulphite is approved in the EU as E225 for use in specific food categories at controlled maximum levels. The key consumer advisory is the allergen declaration requirement: anyone with asthma or a history of sulphite sensitivity should carefully check ingredient labels for E220–E228 and for "contains sulphites" declarations. The allergy risk is independent of the specific sulphite salt used — all sulphite additives contribute to the same pool of SO₂ in food and carry the same advisory.