Labels warn drinkers that wine contains sulfites, and a few wines even advertise themselves as sulfite-free. A small number of people have a strong allergic reaction to sulfites, which makes keeping an eye on sulfite levels very important. However, wines without sulfites face some serious challenges.

Sulfites — a particular type of chemical compound of sulfur and oxygen — occur naturally in wine in very small amounts. During fermentation, winemakers typically add sulfites to wine to prevent spoiling. The sulfites help prevent oxidation; some will dissolve over time, but some remain in the wine. Most wines contain between 25 and 150 parts per million (ppm) of sulfites.

Some people, particularly asthma sufferers, respond to high levels of sulfites in food or wine by experiencing respiratory distress. Symptoms can include coughing or difficulty breathing. Others suffer allergic reactions, including reddening or itchy skin. However, this is fairly rare. Many people also attribute headaches after drinking red wine to high sulfite levels, but this connection is unproven.

Because fermentation naturally produces sulfites, all wines contain some level of sulfites. However, some winemakers produce wines that contain no added sulfites. These may be advertised as sans souffre — French for “without sulfur” — or as “organic,” since U.S. law limits the sulfite levels of wines marketed as “organic.”

However, low-sulfite wines have their own problems; because they lack sulfites, they’re very vulnerable to oxidation and therefore don’t age well. Young wines are less likely to be spoiled. Red wine may also be safer; although red wine without added sulfites is still more vulnerable to spoiling than red wine with sulfites, its high tannin levels will act as a partial preservative.

American wineries producing wine without added sulfites include Frey Vineyards, Donkey & Goat and Badger Mountain; imported wines that keep sulfites to a minimum include some of those produced by Domaine Valentin Zusslin and Ch√Ęteau le Puy.