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Potassium metabisulfite

Potassium metabisulfite
Other names Potassium pyrosulfite
Dipotassium disulfite
Molecular formula K2S2O5
SMILES [O-]S(=O)OS(=O)[O-].[K+].[K+]
Molar mass 222.32 g·mol−1
Appearance White crystalline powder
with pungent odour
CAS number 16731-55-8
Density and phase 2.34 g/cm3, solid
Solubility in water 45 g/100 ml (20 °C)
Melting point 190°C
MSDS External MSDS
NFPA 704
EU classification Error creating thumbnail: Xi
R-phrases R36, R37, R38
S-phrases S26, S39
RTECS number TT4920000
Except where noted otherwise, data are given for
materials in their standard state (at 25 °C, 100 kPa)
Infobox disclaimer and 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 sulfite 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)




Potassium metabisulfite is a common wine or must additive, where it forms sulfur dioxide gas (SO2). This both prevents most wild microorganisms from growing, and it acts as potent antioxidant, protecting both the color, and delicate flavors of wine.

Typical dosage is 1/4 tsp potassium metabisulfite per 6 gallon bucket of must (yielding roughly 75 ppm of SO2) prior to fermentation, and 1/2 tsp per 6 gallon bucket (150 ppm of SO2) at bottling.

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 yeasts, bacteria, and fungi. This is called 'stabilizing'. 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. (A.J. DeLange)

See also

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Potassium_metabisulfite". A list of authors is available in Wikipedia.
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