Potassium Metabisulphite

Potassium metabisulfite is a food preservative, which preserves the natural colour of food and protects food against bacteria. The winemaking industry uses it as an additive during the bottling process.

Synonyms
Potassium pyrosulphite, Dipotassium disulfite, Dipotassium disulphite, Dipotassium Disulphite, E 224, PBMS, Potassium Pyrosulfite
Chemical Formula
K2O5S2
CAS Number
16731-55-8

Characteristics

Molar Weight
222.312 g/mol
Melting Point
190 °C
Density
2.34 g/cc
Forms
Powder, White, Yellow, Pale, Crystalline

Uses and Applications

Key applications

  • Dyes
  • Food preservatives
  • Food additive
  • Antibacterial
  • Reducing agent
  • Wine production
  • Bleaching agent

Potassium Metabisulphite (Potassium disulphite)

Potassium disulphite is a synthetically produced chemical compound that does not occur in nature. It is mainly used in the food industry and wine production as a preservative.

Properties of potassium disulphite

Potassium disulphite is a white-yellow solid with a sulphur-like odour, which exists as a crystalline powder. It dissolves easily in water, but is almost insoluble in alcohol.
The chemical compound from the disulphite group is a salt of disulphuric acid. Potassium disulphite breaks down into potassium sulphate and sulphur dioxide on contact with water or acids. The latter is responsible for the antioxidant and antimicrobial properties of the compound.
Potassium disulphite is usually produced by chemical reactions using sulphur dioxide and a potassium compound such as potassium hydroxide or potassium carbonate. In the production with potassium hydroxide, sulphur dioxide is introduced into an aqueous solution of potassium hydroxide, producing potassium disulphite and water. In the production with potassium carbonate, sulphur dioxide is reacted with potassium carbonate. In addition to potassium disulphite, carbon dioxide is formed as a by-product.
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Potassium disulphite in the food industry

Potassium disulphite is mainly used in the food industry as a preservative and antioxidant under the name E 224. It is subject to certain maximum quantity restrictions.
Potassium disulphite works by releasing sulphur dioxide, which inhibits the growth of bacteria, yeasts and moulds and thus preserves food. It also has an antioxidant effect, preventing oxidative processes that affect the taste, colour and quality of food. As an antioxidant that binds free oxygen molecules, it extends the shelf life of ready meals and canned foods such as potato products or seafood, which oxidise easily.
Potassium disulphite also stops the enzymatic browning of foods such as fruit. It has a colour-stabilising effect and preserves the light colour of products such as dried fruit and fruit juices. Potassium disulphite is also known as dumpling white or dumpling aid. It prevents dumplings from turning grey during processing.
Potassium disulphite is used for stabilisation in wine production. It inhibits undesirable microorganisms during fermentation. It prevents oxidation, which keeps the wine fresh for longer. It also ensures that the original taste and colour are retained.
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Potassium disulphite in the textile industry

Potassium disulphite is used in the textile and dyeing industry as a reducing agent, especially when dyeing fabrics with indigo. Indigo is a natural blue dye that is poorly soluble in its oxidised form and attaches to fibres only with difficulty. By using potassium disulphite, indigo is converted into its reduced form, which is water-soluble and attaches better to textile fibres.
Potassium disulphite is also used for colour fixation. It stabilises the binding of dyes to the fibres and improves the colour intensity. As an oxidation inhibitor, potassium disulphite prevents dyes from oxidising prematurely and thus losing their dyeing power.
Potassium disulphite is also used in the textile industry to treat textiles before dyeing. It helps to remove certain substances or impurities from the fabrics that could affect the dyeing result.
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Potassium disulphite in the construction industry

In the construction industry, potassium disulphite is mainly used in concrete processing and cement production. It is added to concrete plasticisers or concrete retarders and enables improved control of concrete curing and processing, which is particularly relevant in hot climates or for large construction projects.
In the cement industry, potassium disulphite is used to delay the hydration process of cement.
Potassium disulphite also acts as an ingredient in cleaning agents to remove concrete residues from equipment or machinery. It is also an ingredient in corrosion inhibitors to prevent rust formation on iron or steel parts for construction projects.
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Potassium disulphite in the cleaning industry

In the cleaning industry, potassium disulphite is used in specialised areas such as disinfection in food processing and the removal of discolouration. Direct use in the household or as a general cleaning agent is unusual.
For example, potassium disulphite serves as a source of sulphur dioxide, which is used in certain disinfection processes against microorganisms such as bacteria, yeasts and mould, for example when cleaning wine or food storage tanks.
Surface cleaning solutions can contain potassium disulphite to remove or prevent oxidation-related stains or discolouration.

Potassium disulphite in the polymer industry

In the polymer industry, potassium disulphite acts as a reducing agent and initiator in certain polymerisation reactions such as radical polymerisation. It helps to start or control the reactions necessary to combine monomers into polymers.
Potassium disulphite is also used to prevent oxidation in polymers, especially in the processing of plastics. It supports the stability of polymers and extends the service life of plastic products.
In certain applications, potassium disulphite modifies the surface of coated or finished plastics, among other things.
It is also used in rubber and latex production to control or stabilise the polymerisation process.

Potassium disulphite in water treatment

The sulphur dioxide released by potassium disulphite acts as a reducing agent and plays a role in various water treatment processes.
In water treatment, potassium disulphite is used for dechlorination. It removes residual chlorine or chloramines from the water. This is relevant for the food industry, aquaculture, drinking water treatment and waste water treatment, for example.
Potassium disulphite is also used in water treatment to remove oxygen. It reduces dissolved oxygen in water, which causes corrosion in pipes, boilers or other systems.
In industrial applications, potassium disulphite is used to control the oxidation process, for example in the treatment of process water.

Other areas of application for potassium disulphite

Potassium disulphite is used in the pharmaceutical industry due to its antioxidant and preservative properties. It ensures the stability of active ingredients and extends the shelf life of medicines. It is used both in finished preparations and during production.
In agriculture, potassium disulphite is used in the storage, preservation and processing of agricultural products. For example, it protects freshly harvested grapes for consumption or for wine production from microbial decomposition during storage and transport, and potatoes or apples from enzymatic browning.
In animal nutrition, potassium disulphite is used to preserve animal feed such as maize or grass silage, cereals or fishmeal. It also acts as an antioxidant that prevents the degradation of sensitive nutrients such as vitamins or fatty acids in animal feed.