What are sulfites exactly...

Sulfites (also sulphites) are sulfur-containing compounds (typically Sulfur Dioxide - SO2) that are used as food preservatives. Winemakers use sulfites to keep wine from spoiling. Sulfites arrest the metabolic processes of yeasts and bacteria. They prevent microbial growth, keep the color bright, fruit flavors fresh, and prevent spoilage. However, all wines (even those that have not had sulfites added by the winemaker) contain small amounts of sulfites, which are produced naturally by yeast during fermentation.

Sulfites from any source, food or wine, are harmful to about .25% of the population. The US Food and Drug Administration (FDA), which keeps track of reported sulfite reactions in the U.S., listed just 1,097 such cases between 1985 and 1995. Although the threat is small, since 1987 the FDA has required that all wines containing more than 10 parts per million of sulfites must bear a warning label that says "Contains Sulfites.” Anything below that level does not need to have the label, but it still may contain sulfites.

There’s a common perception that sulfur additions are a modern American technique. Sulfites have been used to preserve food and beverages since the 17th century in Europe and in the U.S. since the early 1800’s. Sulfites are present in numerous other foods and beverages, including: fruit juice, dried fruits and vegetables, molasses, shrimp, sauerkraut, pickles, corn syrup, vinegars, packaged gravies and sauces, and many salad bar items.

Sulfites Separating Fact from Fiction
GOOSECROSS-Sulfites and Wine