It has been known for many years that sulfur compounds are particularly aggressive in imparting unwanted changes in the flavor of the product. Historically, a "Taste Test" has been used on the final product. It can screen against the release of poor taste, but cannot guard against the use of contaminated raw materials used in the final formula. Carbon dioxide is a raw material added during the bottling process. It is required to be extremely pure. Many of the possible impurities are limited to less than 1.0ppm in total content. Sulfur components are held to an even lower specification. Typically, a specification for hydrogen sulfide or carbonyl sulfide can be as low as 50ppb maximum.