What is sodium metabisulfite?

Sodium Metabisulfite is listed as an ingredient used in the Beefy Melt flour tortilla. Also known as sodium pyrosulfite, sodium metabisulfite is an inorganic white crystalline powder used as a disinfectant, antioxidant, and food preservative. More specifically, it is the salt produced from sulphurous acid (sulfur dioxide is mixed with water). Sodium Metabisulfite (SMBS) is used as a bleaching agent to create brighter, fresher colors in foods. It's also used to reduce oxidation and block microorganisms from forming in foods, thus increasing shelf life. The additive is commonly found in baked goods, potato chips, dried fruit, tortilla doughs, and other processed foods.