Sodium metabisulfite (Na2S2O5) structure, properties, uses, risks

Philip Kelley
Sodium metabisulfite (Na2S2O5) structure, properties, uses, risks

The sodium metabisulfite is an inorganic compound formed by two sodium Na ions+ and a metabisulfite or disulfite ion StwoOR5two-. Its chemical formula is NatwoStwoOR5. It is a white crystalline solid. It is used as an antioxidant and antimicrobial agent in a variety of pharmaceuticals and functions as a preservative in many food preparations.

The NatwoStwoOR5 It is used to treat the flour to make cookies and pastry candies as it helps to break down protein molecules and make the dough easier to shape and does not shrink when cut into smaller pieces.

Na sodium metabisulfitetwoStwoOR5 solid. No machine-readable author provided. Walkerma assumed (based on copyright claims). [Public domain]. Source: Wikimedia Commons.

It is used in many processed foods to prevent them from being attacked by fungi and bacteria. These foods include cheeses, fruit juices, sauces, margarines, etc..

However, since some negative effects on human health have been noted, the maximum amount of sodium metabisulfite Na is controlled by licensed bodies.twoStwoOR5 what these foods should contain.

The other applications of NatwoStwoOR5 are generally based on their reducing properties (the opposite of oxidant), such as to reduce the amount of chlorine in treated water, as wool bleach, in cosmetic formulas, among other uses.

Article index

  • 1 Structure
  • 2 Nomenclature
  • 3 Properties
    • 3.1 Physical state
    • 3.2 Molecular weight
    • 3.3 Melting point
    • 3.4 Specific weight
    • 3.5 Solubility
    • 3.6 pH
    • 3.7 Chemical properties
  • 4 Obtaining
  • 5 Uses in food
    • 5.1 As a preservative
    • 5.2 In the wine and other beverage industry
    • 5.3 To treat some flours, cereals and starches
    • 5.4 Foods that should not be used
  • 6 Other uses
  • 7 Risks
  • 8 References


Sodium metabisulfite is made up of two sodium ions Na+ and a bisulfite ion StwoOR5two-. The latter has two sulfur atoms attached to each other and five oxygen atoms distributed between them..

Chemical structure of sodium metabisulfite NatwoStwoOR5. Author: Benjah-bmm27. Source: Wikimedia Commons.


-Sodium metabisulfite

-Sodium pyrosulfite

-Sodium disulfite

-Disodium disulfite


Physical state

Colorless, white or yellowish crystalline solid. Hexagonal crystals.

Molecular weight

190.11 g / mol

Melting point

At temperatures above 150 ° C it decomposes.

Specific weight

1.4 at 25 ° C / 4 ° C


Very soluble in water: 66.7 g / 100 g of water.


Its aqueous solutions are acidic. A 10% solution has a pH of 4.0-5.5.

Chemical properties

When dissolved in water, it is a corrosive acid. Has reducing and antioxidant properties.

If exposed to air it slowly oxidizes to sodium sulfate NatwoSW4, also losing part of its SO contenttwo.

Reacts with water to give sodium bisulfite NaHSO3, sulfur dioxide SOtwo and sodium sulphite NatwoSW3.

It has a slight smell of sulfur. It is not combustible, but when subjected to heat it can generate toxic gases.


Sodium metabisulfite can be obtained by passing an excess of the sulfur dioxide gas SOtwo by a solution of sodium carbonate NatwoCO3.

Uses in food

As a preservative

The NatwoStwoOR5 it is an antioxidant. It serves as a preservative and inhibitor of certain microorganisms. Its antimicrobial effect is optimal below pH = 4, as in fruit juices.

It helps prevent spoilage and slow the blackening of certain foods. It has been used for example to prevent the browning of sweet potatoes.

It is used during the harvest of marine shrimp to prevent the formation of black spots. Shrimp are dipped in a metabisulfite solution on ice.

Shrimp are sometimes dipped in aqueous sodium metabisulfite solution to prevent spoilage. Author: Aakashkhatu1998. Source: Pixabay.

It is an effective antioxidant and improves the retention of ascorbic acid (vitamin C) in dried fruits and juices. In these it inhibits certain types of bacteria, fungi and yeasts.

It has been used in South Africa to control spoilage and inhibit browning of lychee fruit. However, it seems that the flavor of said fruit changes slightly..

Other foods in which it is used are cheese, various drinks, margarine, sauces, sweets and fish.

In the wine and other beverage industry

In grapes after harvest it is used as a fungicide, since certain fungi can grow on this fruit. It then acts on certain specific microorganisms, which makes it useful in the wine industry as it allows controlling its fermentation..

Residual metabisulfite is effective after wine fermentation to prevent the growth of alcohol tolerant yeasts.

It has also been used in apple juice and cider to control certain pathogenic microorganisms such as Escherichia coli.

To treat some flours, cereals and starches

It is used to condition the dough of some baked goods. It acts as a reducing agent in the manufacture of cookies, especially those low in fat and low in sugar, and in pastry sweets..

Metabisulfite reacts with the S-S sulfur bonds of the proteins contained in the flour of the dough with which cookies and sweets are prepared, softening it, making it more extensible and less elastic.

One of the goals is to prevent the dough from shrinking, either before or during baking. However, its use in cookie dough is not always accepted and other alternatives are preferred..

Some cheeses, jams, and crackers may contain sodium metabisulfite as a preservative. Author: Steve Buissinne. Source: Pixabay.

Also serves to bleach edible starches and to soften corn kernels during the wet milling process.

Foods that should not be used

The United States Food and Drug Administration, or FDA Food and Drug Administration) Labeled sodium metabisulfite NatwoStwoOR5 as a "generally safe" substance.

However, it has been recognized by the body as an antithiamine or antivitamin B1 compound..

Therefore it should not be used in meats, or in foods that are a source of vitamin B1. Nor should it be used on fruits or vegetables that are sold raw to consumers or that are presented as fresh..

According to some consulted sources, if it is used in concentrations higher than 10 mg / Kg of food, it must be reported on the label of this.

Other uses

Other applications of NatwoStwoOR5 below.

-As a reducing agent in cosmetic formulas and as an antioxidant for example in hair care products.

-As an antioxidant in pharmaceutical preparations, such as syrups or injectable fluids. It is used in acid preparations. Has some antimicrobial activity, especially at acid pH.

-As a laboratory reagent, for example to preserve histamine when testing is done.

Some liquid medicines may contain NatwoStwoOR5 as a preservative. Author: Steve Buissinne. Source: Pixabay.

-As a reducing agent in photo development.

-To reduce chlorine in industrial process water and in wastewater treatment.

-In the textile industry: as a wool bleach, as an antichloro agent after nylon bleaching, to reduce some dyes and to solubilize others.

-To produce sulfur dioxide SOtwo on the site of use. For example in silos of fresh grass, the SOtwo produced by sodium metabisulfite develops acidity quickly and allows the conservation of the material, since the fermentation would take too long.

Wool can be bleached with sodium metabisulfite. Author: JacLou DL. Source: Pixabay.


-If Na is inhaledtwoStwoOR5 solid is toxic. Direct contact strongly irritates the skin, mucous membranes and tissues. It is irritating to the eyes and respiratory system.

-If ingested directly, it can cause abdominal pain, diarrhea, nausea and vomiting..

-Is corrosive.

-Some asthmatics are said to be dangerously sensitive to minute amounts of metabisulfite in food.

-It is harmful to aquatic organisms.


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  2. U.S. National Library of Medicine. (2019). Sodium metabisulfite. National Center for Biotechnology Information. Recovered from
  3. Sivakumar, D. and Korsten, L. (2011). Litchi (Litchi chinensis Sonn.). In Postharvest Biology and Technology of Tropical and Subtropical Fruits: Cocona to Mango. Recovered from
  4. Danyluk, M.D. et al. (2012). Microbial decontamination of juices. In Microbial Decontamination in the Food Industry. Recovered from
  5. Wieser, H. (2012). The use of redox agents in breadmaking. In Breadmaking (Second Edition). Recovered from
  6. Ercan, S. et al. (2015). Induction of omega 6 inflammatory pathway by sodium metabisulfite in rat liver and its attenuation by ghrelin. Lipids in Health and Disease (2015) 14: 7. Recovered from

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