Potassium metabisulphite

Potassium metabisulphite (also written potassium metabisulfite) is a white crystalline powder that releases sulphur dioxide when dissolved or acidified. It is one of the most widely used sulphiting agents in food and beverage production, particularly in winemaking where it is the standard antimicrobial and antioxidant treatment applied to barrels, equipment, and must. It also preserves dried fruit, jams, fruit juices, and dehydrated potato products.

JECFA's ADI is 0.7 mg per kilogram body weight per day expressed as SO₂ equivalents, evaluated in 1967 — shared across the sulphite family (E220–E228). The primary health concern is sulphite-triggered asthma, which affects a meaningful proportion of asthma sufferers. Wine, which can contain significant sulphite levels from both natural fermentation and addition, is a well-documented trigger for sulphite-sensitive individuals.

Potassium metabisulphite is approved in the EU, US (GRAS), UK, Australia, Japan, and Vietnam. EU regulations mandate sulphite declaration on labels at levels above 10 mg/kg or 10 mg/L SO₂ equivalents. Wine is required to carry "contains sulphites" labelling regardless of the form used. Dried apricots, sultanas, and similar dried fruits are often among the highest sulphite-containing foods available to consumers. People with sulphite sensitivity — especially asthmatic consumers — should be aware that E224, like all sulphiting agents, is a declarable allergen across all major food markets.