Potassium metabisulfite

Potassium metabisulfite
Other names Potassium pyrosulfite Dipotassium disulfite
Identifiers
CAS number	16731-55-8 Y
PubChem	28019
ChemSpider	26061 Y
UNII	65OE787Q7W Y
RTECS number	TT4920000
Jmol-3D images	Image 1
SMILES [K+].[K+].[O-]S(=O)S([O-])(=O)=O
InChI InChI=1S/2K.H2O5S2/c;;1-6(2)7(3,4)5/h;;(H,1,2)(H,3,4,5)/q2*+1;/p-2 Y Key: RWPGFSMJFRPDDP-UHFFFAOYSA-L Y InChI=1/2K.H2O5S2/c;;1-6(2)7(3,4)5/h;;(H,1,2)(H,3,4,5)/q2*+1;/p-2 Key: RWPGFSMJFRPDDP-NUQVWONBAF
Properties
Molecular formula	K2O5S2
Molar mass	222.32 g mol−1
Appearance	White crystalline powder
Odor	pungent (sulfur dioxide)
Density	2.34 g/cm3 (solid)
Melting point	190 °C decomp.
Solubility in water	450 g/l (20 °C)
Solubility	insoluble in ethanol
Hazards
MSDS	ICSC 1175
EU Index	Not listed
R-phrases	R36 R37 R38
Main hazards	Irritant, asthma risk
NFPA 704	0 1 0
Related compounds
Other anions	Potassium bisulfite Potassium sulfite
Other cations	Sodium metabisulfite
Y metabisulfite (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Potassium metabisulfite, K₂S₂O₅, 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.

Potassium metabisulfite has a monoclinic crystal structure which decomposes at 190°C, yielding potassium oxide and sulfur dioxide:

K₂S₂O₅(s) → K₂O(s) + 2SO₂(g)

Uses

It is used as a food additive, also known as E224.^[1] It is restricted in use^[2] and may cause severe allergic reactions in sensitive persons.^[3][4]

Potassium is an inhibitor of the polyphenol oxidase enzyme.^[5]

Wine

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.

The typical dosage is 1/4 tsp potassium metabisulfite per six-gallon bucket of must (yielding roughly 75 ppm of SO₂) prior to fermentation; then 1/2 tsp per six-gallon bucket (150 ppm of SO₂) at bottling. Most commercial wineries do not add more than 30ppm at bottling.

Winemaking equipment is sanitized by spraying with a 1% SO₂ (2 tsp potassium metabisulfite per L) solution.

Beer

Potassium metabisulfite is sometimes used in the brewing industry to inhibit the growth of wild yeasts, bacteria, and fungi. This is called 'stabilizing'. It is also used to neutralize chloramine that has been added to tap water at the source as a disinfectant. 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 anyway. It can also be added to strike water (the water used to mash the barley) in order to remove chloramines which can cause phenolic off flavors in beer.

Other uses

• 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.^[6]

See also

• Campden tablets

References

1. ^ List of E-number food additives
2. ^ http://www.foodreactions.org/allergy/additives/200.html
3. ^ Metcalfe, Dean D.; Simon, Ronald A. (2003). Food allergy: adverse reactions to food and food additives. Malden, MA: Wiley-Blackwell. pp. 324–339. ISBN 0632046015. 
4. ^ Nordic Food Additive Database
5. ^ 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. 
6. ^ http://encyclopedia2.thefreedictionary.com/potassium+metabisulfite