Sodium Metabisulfite

About This Product

Sodium metabisulfite, also called sodium disulphite or sodium pyrosulphite, is authorised as food additive E223 in the EU and UK. Its CAS number is 7681-57-4, its formula Na2S2O5 and its molar mass 190.1 g/mol. Food grades are white to slightly yellowish crystalline powders with a sulphur dioxide odour. In water and acidic foods it releases sulphur dioxide and bisulphite, which provide its effects; theoretically 1 kg yields about 0.674 kg of SO2.

Sulphites have several functions at once. They inhibit yeasts, moulds and bacteria, they are antioxidants, and they block both enzymic browning and non-enzymic browning. Typical applications include dried fruit, fruit pulps and juices held for further processing, dehydrated potato and vegetable products, crustaceans such as prawns, where they prevent black spot, and a limited number of meat products where specifically permitted. Winemaking and cider making use sulphites under their own product rules. In some markets sodium metabisulfite is also used where permitted to relax gluten in hard, laminated biscuits. Dosage is set by the free or total SO2 target for the product and process, not by a fixed addition rate.

Several limitations shape its use. Sulphites destroy thiamine (vitamin B1), so their use in foods that are significant sources of it is restricted. SO2 can leave a sharp taste and odour, and it bleaches some colours. Above 10 mg/kg or 10 mg/litre, expressed as SO2, sulphites must be emphasised as an allergen on the label under Regulation (EU) No 1169/2011 and the UK retained equivalent, which matters for products sold to consumers with sulphite sensitivity.

Buyers typically agree the assay as Na2S2O5 and the equivalent SO2 content, iron, selenium, thiosulphate, arsenic and lead, together with appearance and water-insoluble matter. The grade should conform to the E223 purity criteria in Regulation (EU) No 231/2012 and its GB equivalent, or to FCC or JECFA where required. Because SO2 strength declines in storage, agree the minimum assay at delivery and a sensible use-by period.

Permitted categories and maximum levels for E220 to E228 are set in Annex II of Regulation (EC) No 1333/2008 and the UK retained equivalent, expressed as SO2 and covering all sources in the food. Categories are narrowly defined and differ between markets, so check the current annex for the exact product. On the label use preservative or antioxidant with the name or E223, and emphasise sulphites in the ingredients list when the threshold is exceeded.

Sodium metabisulfite is classified as harmful if swallowed and as causing serious eye damage, and contact with acids releases toxic SO2 gas; read the safety data sheet, provide ventilation and eye protection, and keep it away from acids. Store tightly sealed in a cool, dry place and rotate stock, because air and moisture oxidise it to sulphate. When you enquire, give the application, SO2 target, the minimum assay required, pack size, volume and destination.