Sulfites are a harmless natural compound found in all wines that commonly added to a vintage in order to preserve its condition, preventing any further fermentation, protecting it from spoilage or further oxidation. Sulfur dioxide (SO₂) also safeguards your wine any bacterial machinations. Sulfites are monster hunters, stopping your delicious grape liquid from becoming vinegar.
Organic wines tend to have lower levels of sulfites and are regulated to possess less than regular wines. Further, white wines and sweeter wines have more sulfites than red and dry wines.
Within the U.S.A., the label of any wine bottled after the middle of 1987 must state if its sulfite content exceeds 10 parts per million. The E.U. established a similar regulation in November of 2005.