Potassium metabisulfite
Potassium metabisulfite
Other names
Potassium pyrosulfite
Dipotassium disulfite
Potassium metabisulphite
Dipotassium disulphite
3D model (JSmol)
ECHA InfoCard 100.037.072 Edit this at Wikidata
E number E224 (preservatives)
RTECS number
  • TT4920000
  • InChI=1S/2K.H2O5S2/c;;1-6(2)7(3,4)5/h;;(H,1,2)(H,3,4,5)/q2*+1;/p-2 checkY
  • InChI=1/2K.H2O5S2/c;;1-6(2)7(3,4)5/h;;(H,1,2)(H,3,4,5)/q2*+1;/p-2
  • [K+].[K+].[O-]S(=O)S([O-])(=O)=O
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):
Main hazards
Irritant, asthma risk
GHS labelling:
GHS05: CorrosiveGHS07: Exclamation mark
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)
NFPA 704 four-colored diamondHealth 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
Safety data sheet (SDS) ICSC 1175
Related compounds
Other anions
Potassium bisulfite
Potassium sulfite
Other cations
Sodium metabisulfite
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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.[1] 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.

Preparation and reactions

Main article: bisulfite § Reactions

Potassium metabisulfite can be prepared by treating a solution of potassium hydroxide with sulfur dioxide.[2]

2 SO2 + 2 KOH → K2S2O5 + H2O

It decomposes at 190 °C, yielding potassium sulfite and sulfur dioxide:

K2S2O5 → K2SO3 + SO2


It is used as a food additive, also known as E224.[3] It is restricted in use and may cause allergic reactions in some sensitive persons.[4]


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.[5]

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.

Other uses

See also


  1. ^ Barberá, José Jiménez; Metzger, Adolf; Wolf, Manfred (2000). "Sulfites, Thiosulfates, and Dithionitesl Chemistry". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a25_477. ISBN 978-3527306732.
  2. ^ Johnstone, H. F. (1946). "Sulfites and Pyrosulfites of the Alkali Metals". Inorganic Syntheses. Inorganic Syntheses. Vol. 2. pp. 162–167. doi:10.1002/9780470132333.ch49. ISBN 9780470132333.
  3. ^ List of E-number food additives
  4. ^ 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.
  5. ^ "The Truth About Sulfites in Wine & the Myths of Red Wine Headaches".
  6. ^ "Potassium Metabisulfite".
  7. ^ "Color Metallography". 2011-05-04.