| Potassium metabisulfite | |
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Other names
Potassium pyrosulfite |
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| Identifiers | |
| CAS number | 16731-55-8 |
| PubChem | 28019 |
| ChemSpider | 26061 |
| UNII | 65OE787Q7W |
| RTECS number | TT4920000 |
| Jmol-3D images | Image 1 |
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| 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
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| Related compounds | |
| Other anions | Potassium bisulfite Potassium sulfite |
| Other cations | Sodium metabisulfite |
| (verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
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.
Potassium metabisulfite has a monoclinic crystal structure which decomposes at 190 °C, yielding potassium oxide and sulfur dioxide:
Contents |
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]
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.
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.
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