Sulfites (also sulphites) are compounds that contain the sulfite ion SO2-3 (additive IUPAC name: trioxidosulfate(2-)). The sulfite ion is the conjugate base of sulfurous acid. Although the acid itself is elusive, its salts are widely used. Sulfites occur naturally in all wines to some extent. Sulfites are commonly introduced to arrest fermentation at a desired time, and may also be added to wine as preservatives to prevent spoilage and oxidation at several stages of the winemaking. In the United States, wines bottled after mid-1987 must have a label stating that they contain sulfites if they contain more than 10 parts per million. In the European Union an equivalent regulation came into force in November 2005. Organic wines are not necessarily sulfite-free.  Other food Sulfites are often used as preservatives in dried fruits, and dried potato products. Most beers no longer contain sulfites. Although shrimp is sometimes treated with sulfites on fishing vessels, the chemical may not appear on the label. In 1986, the Food and Drug Administration in the United States banned the addition of sulfites to all fresh fruit and vegetables that are eaten raw.