The Effect of Sulfur Dioxide on Saccharomyces cereviseae.

The wine industry dates back to at least 3000 BC. (Amerine and Singleton, 1977) but it was not until the 1830's that Cagniard de Latour, Kutzing and Schwann discovered that the growth of yeast and protists was responsible for wine and other fermentations (Pirt, 1975). Sulfur dioxide has been used since antiquity as a sterilant for equipment used in wine making in some cases (Ough, 1983, 1986). Wooden tanks and barrels have been, and still are, sterilized by burning elemental sulfur in them (Ough, 1986). Elemental sulfur is common in volcanic areas (Ough, 1983). The purpose of sulfur dioxide is to inhibit polyphenol oxidase enzymes and to inhibit the growth of wild yeast or bacteria that may be present in fruit juice (Ough, 1986). Bacteria are much more sensitive to sulfur dioxide than yeast or molds (Ouch, 1983). Increased sulfur dioxide concentrations in plumb must decreased the use of soluble solids by the yeast Shizosaccharomyces pombre (Joshi et al., 1991), which may inhibit its growth. Sulpher dioxide also partially protects wine from the destructive action of hydrogen peroxide (Ough, 1986). Sulfur dioxide is usually added to the grapes during or immediately after crushing at levels between 35-100mg/L depending on the condition of the grapes (Ough, 1986). The final level of sulfur dioxide is also adjusted when the fermentation is complete and/or before bottling of the wine. While sulfur dioxide has been used in wines for the past century and the levels of the molecular form which are required to kill yeast and bacteria have been known for almost 20 years, the minimum levels required have not been determined for wine yeast commonly used today. There is also a need to better understand the kinetics and rates of killing, especially at low but useful levels.