sulfur dioxide (SO2)

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A colorless, water-soluble, nonflammable gas used viticulturally in small, controlled amounts through a process called sulfiting. Winemakers use sulfur dioxide in a variety of ways. Grapevines can be sprayed with it to deter many insects and diseases. After the grapes are crushed, sulfur dioxide is used to inhibit the growth of bacteria, mold, and wild yeasts in MUST. It’s also used to prevent spoilage or OXIDATION in the finished wine. There are several ways to introduce sulfur dioxide. It can be added to wine as a gas or as POTASSIUM METABISULFITE, often in the form of Campden tablets. It reacts with the natural acids in grapes to create sulfur dioxide gas. Sulfur wicks can be burned to create sulfur dioxide in empty or partially filled wine barrels to prevent the growth of mold. During such processes, some sulfur dioxide combines with the wine, in which case it’s called fixed (or bound) sulfur dioxide; it has no odor so isn’t noticeable. Free sulfur dioxide is that which doesn’t combine with wine. Excessive amounts of it can produce an undesirable trait indicated by a slight biting sensation at the back of the throat and in the upper part of the nose. Total sulfur dioxide includes all bound and free sulfur dioxide in wine, the allowed amounts of which are regulated by law. See also HYDROGEN SULFIDE; ORGANIC WINE; SULFITES.