What is this compound found in most wines?

Sulfur dioxide is a naturally occurring compound. It is formed from sulfur and oxygen during the fermentation process. It is present in very small quantities. Some winemakers will add it to wine.

Sulfur dioxide is the penicillin of wine, preventing and curing all sorts of ills. One of the most important jobs of sulfur dioxide is to prevent the wine from turning to vinegar. It acts as an antioxidant, keeping wines fresh. It does this by preventing bacterial growth. In sweet wines sulfur dioxide prevents the yeast from refermenting in the bottle.

But, a little goes a long way. Wine makers try not to add anything to wine unless absolutely necessary. So, a light hand is used when adding sulfur dioxide to wine.

With the advent of highly complex and highly technical wine making equipment wine makers don't rely on sulfur dioxide as much as in the past. The irony is that labels in the United States contain the phrase, "Contains Sulfites."

In 1988 Congress passed a law requiring that phrase on the label. Sulfur dioxide didn't suddenly appear in wine in the 1980s. It has been present in its natural and added forms long before 1988. There is now less sulfur dioxide in wines than before the labeling requirement.

Why the concern over sulfites in wine? About 5% of asthmatics are extremely sensitive to sulfites. To allow them to make good health choices, Congress required wines containing more than 10 parts per million of sulfites be labeled with "Contains Sulfites." To keep this in perspective, remember that 10-20 parts per million occur naturally in wine. So, almost every wine will be required to carry this phrase. (Studies have been conducted that suggest that some people may be having reactions to other things than the sulfite in wine.)

Sulfite levels in wine range from about 100-150 parts per million (about the same as dried fruit). You can sometimes ingest more sulfites by eating pizza and drinking diet cola. The maximum allowed by law in the United States is 350 parts per million.

When selecting wines you can look for wines that state "No Sulfites Added." Some assume that organic wines will not contain added sulfites. This is not true. Some organic vintners add as much sulfur dioxide as conventional wineries. New laws have clarified labeling requirements.