Chapter 18

Sulfur Dioxide and Winemaking

(book excerpts)

Sulfur dioxide is added periodically throughout the winemaking process and plays a critical role in quality winemaking. Sulfur dioxide is known by a variety of different names to winemakers, the most common being sulfur dioxide, metabisulfite, and just plain sulfite. Sulfur dioxide is the most common additive in winemaking, because of its multifunctional properties; inhibition of unwanted microorganisms, preventing oxidation, and inhibition of enzymatic and non-enzymatic browning reactions and contribution to wine quality. Sulfur dioxide exists in free and bound forms within wine - but it is the free sulfur dioxide that has the important antioxidant and antimicrobial properties. Therefore, when measuring the sulfur dioxide concentration of a wine, it is the free sulfur dioxide concentration that is generally regarded as the most important. The amount of sulfur dioxide in the free form, and the effectiveness of the free sulfur dioxide, depends on the pH of the wine. The higher the pH, the less sulfur dioxide will be in the useful free form AND the less effective this free sulfur dioxide will be. There are a number of techniques that are used to measure the concentration of sulfur dioxide in wine. Automated systems are available and offer considerable benefits to laboratories that routinely analyze relatively large numbers of samples. Sulfur dioxide may be applied in powder form, as an aqueous solution, or as a gas. Otherwise, sulfur can be applied by the combustion of sulfur wicks or discs.

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