Sulphur Dioxide or SO2 is a compound commonly found in wine. Sulphur is commonly found in wine in small amounts however Sulphur can be added to the wine at various stages of fermentation to protect from effects such as oxygen exposure. All wines contain Sulphur dioxide in them collectively known as sulphites. However, due to the unique nature of each individual wine, those running the fermentation and quality process cannot simply add a generic or standard amount of SO2. The levels added are affected by the amount of SO2 that becomes bound to compounds in the wine, and this in turn is determined by the pH levels. The Sulfur dioxide ions that are not chemically bound to other chemicals in solution and thus are free to react with substances are known as Free SO2.