Potassium metabisulfite (called “meta” for short) contains approximately 57% sulfur dioxide (SO2). Indispensible in modern winemaking, it is used by wineries around the world. It is a highly versatile product, providing a convenient and safe method of introducing sulfur dioxide into wine as well as for many other uses. It functions as an antioxidant, an antiseptic, a defense against unwanted enzymes and aldehydes and acts as a preservative in the aging of wine. Usual dose is 1/4 teaspoon per 5 gallons at racking and typically yields about 40 parts per million (ppm). Do not overdose, or the result will be a wine that has the aroma of burnt matches. May also be used as a rinse to sanitize equipment at the rate of 1 teaspoon per quart of water. Replace annually, as it loses strength over time. Sulfur dioxide gas produced by a solution of meta produces highly irritating sulfur dioxide gas and should be avoided by asthmatics. Meta should never be added directly to wine. Instead, it should be dissolved in a small quantitiy of water first and then stirred into the wine.