Most wines are preserved using sulfur dioxide compounds, commonly called sulfites. Wine makers have used surfur dioxide for many years as a wine preservative. While sulfur dioxide is often added to wine, it is also a natural by-product of the fermentation process. Therefore, no wine is entirely free of sulfites.
Although sulfur dioxide has antioxidant properties and helps keep wine fresh, for asthma sufferers and some other individuals, consumption of sulfites can pose a health risk. Consequently, wines containing more than 10 parts per million of sulfur dioxide are identified on the label as containing sulfites. The amount of sulfites wine may contain is strictly regulated.