Sodium metabisulphite food grade is an inorganic compound composed of sodium, sulfur dioxide. Its chemical formula is Na2S2O5. SMBS typically comes in a white, or yellowish-white crystalline powder, which is easily soluble in water, and leaves that familiar sulfur (rotten egg) smell.it is widely used as food preservative in food industry. Sodium meta bisulfite food grade also known asSodium meta bisulfite, SMBS, Sodium meta bisulfate, sodium hydrogen sulphite.