Potassium metabisulfite, K2S2O5, also known as potassium pyrosulfite, is a white crystalline powder with a pungent odour. It is mainly used as an antioxidant or chemical sterilant. As a disulfite, it is chemically very similar to sodium metabisulfite, with which it is sometimes used interchangeably. Potassium metabisulfite has a monoclinic crystal structure.
3D model (JSmol)
|E number||E224 (preservatives)|
CompTox Dashboard (EPA)
|Molar mass||222.31 g·mol−1|
|Appearance||White crystalline powder|
|Odor||Pungent (sulfur dioxide)|
|Density||2.34 g/cm3 (solid)|
|Melting point||190 °C (374 °F; 463 K) decomposes|
|450 g/l (20 °C)|
|Solubility||Insoluble in ethanol|
|Occupational safety and health (OHS/OSH):|
|Irritant, asthma risk|
|H315, H318, H335|
|P261, P264, P271, P280, P302+P352, P304+P340, P305+P351+P338, P310, P312, P321, P332+P313, P362, P403+P233, P405, P501|
|NFPA 704 (fire diamond)|
|Safety data sheet (SDS)||ICSC 1175|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
(what is ?)
Potassium metabisulfite is a common wine or must additive, in which it forms sulfur dioxide (SO2). Sulfur dioxide is a disinfectant. It also acts as a potent antioxidant, protecting both the color and delicate flavors of wine.
A high dose would be 3 grams of potassium metabisulfite per six-gallon bucket of must (yielding roughly 75 ppm of SO2) prior to fermentation; then 6 grams per six-gallon bucket (150 ppm of SO2) at bottling. Some countries regulate the SO2 content of wines.
Winemaking equipment is sanitized by spraying with a 1% SO2 (2 tsp potassium metabisulfite per L) solution.
Potassium metabisulfite is sometimes used in the brewing industry to inhibit the growth of wild bacteria and fungi. This step is called 'stabilizing'. It is also used to neutralize monochloramine from tap water. It is used both by homebrewers and commercial brewers alike. It is not used as much for brewing beer, because the wort is almost always boiled, which kills most microorganisms.
Potassium metabisulfite can irritate skin, eyes, and respiratory tract.