Sodium metabisulfite is a white or yellow crystalline powder or small crystals, with a strong SO2 odor, specific gravity of 1.4, soluble in water, forming an acidic solution. When it comes into contact with strong acids, it releases SO2 and forms corresponding salts. If left in the air for a long time, it oxidizes to Na2S2O6, so the product should not be stored for a long period. Above 150 degrees Celsius, it releases SO2.