What Is Sodium Metabisulfite?

By Sonia Fernandez

You may have seen the name before, maybe on a package of potato chips or raisins: Sodium metabisulfite. But what you might not know is that this common food preservative, with a mouthful of a name, has a number of other uses.

Close up of potato chips spilling out of bag.

What is Sodium Metabisulfite?

Molecular compounds.

Sodium metabisulfite is an inorganic compound composed of sodium, sulfur and oxygen. Its chemical formula is Na2S2O5 . It typically comes in a white, or yellowish-white crystalline powder. It easily dissolves in water, which leaves that familiar sulfur (rotten egg) smell.

Sodium Metabisulfite in Food

Bowl of raisins.

Sodium Metabisulfite is commonly used as a food preservative for dried foods, like potato chips, raisins and apples, as well as fruit concentrate juices. As a food product, the safe daily intake of sodium metabisulfite has been determined to be about .7 grams per kilogram of body weight. However, those with allergies to sulfites – often exhibited by rashes, hives and wheezing - might try to steer clear of this preservative altogether.

Sodium Metabisulfite as a Cleaner

Waitress with tray of beer and wine.

Sodium metabisulfite is also present in wines and beers, as it is used as both a sterilizer and an antioxidant in the process of brewing beer or fermenting wine. If you or someone you know claims to have an allergy to red wine, it's probably because of the presence of sodium metabisulfite.

The chemical is also used in the process of purifying water, cleaning water pipes and reverse osmosis membranes in desalinization equipment as it is an antibacterial.

Sodium Metabisulfite in Other Uses

Photographer in darkroom.

Sodium metabisulfite's acidic and preservative properties also make it an effective substitute for sodium bisulfite, a chemical which is used in traditional darkroom photography. Also, sodium metabisulfite is used as a bleaching agent in pulp and textile manufacture, as well as a reducing agent in pharmaceuticals. It is also a known preservative in cosmetics.

The chemical, in concentrated form, has also been used in landscape gardening as a tree stump remover, as it disintegrates the lignins – chemicals in plant cell walls – in the tree stumps, making them easier to remove.

Toxicity of Sodium Metabisulfite

Woman using an inhaler.

While the allowable ingestion of sodium metabisulfite as a food preservative reduces it to sulfate in the liver, allowing for harmless elimination, excess exposure to the chemical has been known to damage the human immune system. It has also been linked to cancer and reproductive and developmental toxicity. Lesser concerns include neurotoxicity.

Those with asthma and other allergies may also be sensitive to sodium metabisulfite.

Other Names for Sodium Metabisulfite

Close up of package highlighting sodium.

Sodium pyrosulfite; Disodium Salt Pyrosulfurous Acid; Disulfurous acid, disodium salt, Pyrosulfurous acid, disodium salt; Sodium disulfite; Sodium Pyrosulfite; Sodium disulfite; Disodium disulfite