Potassium metabisulfite, K2S2O5, also known as potassium pyrosulfite, is a white crystalline powder with a pungent sulfur odour. The main use for the chemical is as an antioxidant or chemical sterilant. It is a disulfite and is chemically very similar to sodium metabisulfite, with which it is sometimes used interchangeably. Potassium metabisulfite is generally preferred out of the two as it does not contribute sodium to the diet.
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|
|Main hazards||Irritant, asthma risk|
|Safety data sheet||ICSC 1175|
|GHS Signal word||Danger|
|H315, H318, H335|
|P261, P264, P271, P280, P302+352, P304+340, P305+351+338, P310, P312, P321, P332+313, P362, P403+233, P405, P501|
|NFPA 704 (fire diamond)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
- K2S2O5(s) → K2SO3(s) + SO2(g)
Potassium metabisulfite is an inhibitor of the polyphenol oxidase enzyme.
Potassium metabisulfite is a common wine or must additive, in which it forms sulfur dioxide gas (SO2). This both prevents most wild microorganisms from growing, and it 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. Most commercial wineries do not add more than 30 ppm at bottling. Some countries impose regulations on how much SO2 wines are allowed to contain.
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 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 is sometimes added to lemon juice as a preservative.
- Potassium metabisulfite is used in the textile industry for dyeing and cotton printing.
- Potassium metabisulfite is sometimes used to precipitate gold from solution in aqua regia (as an alternative to sodium sulfite).
- It is a component of certain photographic developers and solutions used in photographic fixing.
- It is used as a bleaching agent in the production of Coconut cream.
- It is used in some pickles as a preservative.
- It is used in tint etching iron-based metal samples for microstructural analysis.
Potassium metabisulfite causes skin irritation, serious eye irritation, and may cause respiratory irritation. Hence, it should be manipulated under individual protective elements, such as gloves, coat, mask and glasses. Also, it should be manipulated under alkaline conditions as potassium metabisulfite reacts with acids, releasing toxic gases.
- List of E-number food additives
- Metcalfe, Dean D.; Simon, Ronald A. (2003). Food allergy: adverse reactions to food and food additives. Malden, MA: Wiley-Blackwell. pp. 324–339. ISBN 978-0-632-04601-0.
- Del Signore A, Romeoa F, Giaccio M (May 1997). "Content of phenolic substances in basidiomycetes". Mycological Research. 101 (5): 552–556. doi:10.1017/S0953756296003206.
- "Potassium Metabisulfite".
- "Color Metallography". 2011-05-04.
- "Material Safety Data Sheet". Guidechem.