Sodium bisulfite is a chemical compound with a chemical formula of NaHSO3. It is most commonly used as an additive to food and can be prepared a couple different ways, the most popular of which is bubbling sulfur dioxide in a solution of sodium carbonate in water. When this chemical is in contact with a chlorine bleach solution, generates heat. Sodium bisulfite is one of the weakest acids. It is used by a lot of home winemakers to help preserve the flavor in the wine and can also be used to help prevent browning when it comes to fruit canning. Lastly, sodium bisulfite is added to the leafy greens in salad bars and other places to help keep their freshness.