What Is Sodium Metabisulfite?

You may have seen the name before when browsing the ingredient list on the back of a bag of potato chips or raisins: sodium metabisulfite. But what you might not know is this common food preservative, with a mouthful of a name, has a number of other uses too.

Sodium metabisulfite is an inorganic compound composed of sodium, sulfur and oxygen. It's typically a white, or yellowish-white crystalline powder that easily dissolves in water, which leaves that unpleasantly familiar sulfur smell.

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 - may want to steer clear of this preservative altogether.

The compound is also present in wines and beers, as it's 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.

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

Its acidic and preservative properties also make it an effective substitute for sodium bisulfite, a chemical that's 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's 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.

While the allowable ingestion of sodium metabisulfite as a food preservative reduces it to sulfate in the liver, allowing for harmless elimination, excess exposure has been known to damage the immune system. It has also been linked to cancer, reproductive, developmental toxicity and neurotoxicity. Those with asthma and other allergies may also be sensitive to sodium metabisulfite.

If you're into checking the labels of your food, drinks or household cleaning agents, keep in mind that sodium metabisulfite goes by a number of other names too, including sodium pyrosulfite; disodium salt pyrosulfurous acid; disulfurous acid, disodium salt, pyrosulfurous acid, disodium salt; sodium disulfite; sodium pyrosulfite; sodium disulfite; disodium disulfite.