Sulfur is an antioxidant and antimicrobial that at very low levels is used as a preservative in wine. It serves to keep bacterial activity in check (wine is not pasteurized), preserves color (especially important in white wines), and keeps wine from oxidizing prematurely.
Its use in wine goes back to Roman times. Wines sold in the U.S. must list “contains sulfites” on the label, when sulfur is used in winemaking. Although no such rule applies to other foods including cheeses, dried fruits, or processed french fries, all of which contain far higher levels of sulfites than wine (we can thank neo-prohibitionist politicians in the 1970s for that).
While sulfites in wine may be a problem for a tiny minority of people with allergies or asthma, for most of us sulfites are not an issue. The relationship between sulfites and wine-related headaches has been debunked.
For winemakers, making no sulfites added (NSA) wines is a difficult and risky proposition. When making NSA wine, the winemaking equipment must be sterile, and NSA winemaking techniques often involve the additional use of specialized yeasts, pasteurization, and sterile filtering. In other words, making NSA wines is not exactly non-intervention winemaking.
However, many winemakers have accepted the challenge of making NSA wines (even NSA wines contain residual sulfites, as sulfur dioxide is a byproduct of fermentation), and there is a market for these wines. And, while many NSA wines still seem sterile and stripped of flavor, we are seeing a vast improvement in the quality of these wines in general.