Potassium or sodium metabisulfite are a sulfur-based product that is used primarily in wine, cider and beer making to kill bacteria and to inhibit the growth of most wild yeast: this product is also used to eliminate both free chlorine, and the more stable form, chloramine, from water solutions (i.e., drinking water from municipal sources). It can be used to protect against wild yeast and bacteria without affecting flavour. Typical use contributes 67 ppm sulfur dioxide to the wort but the level of active sulfur dioxide diminishes rapidly as it reacts with chlorine and chloramine, and with aldehydes (particularly in wine). Therefore, the concentration of free sulfur dioxide is greatly diminished by the time the beer or wine is consumed.
