Skip to content
SupplyList
Menu

Sodium sulfite

Sodium sulfite suppliers and sourcing guide

Sodium sulfite is a sodium salt of sulfurous acid, made by passing sulfur dioxide into a sodium carbonate or sodium hydroxide solution and then crystallizing or drying the product. It is sold as an anhydrous white powder or as the heptahydrate. Food processors use it as a sulfiting agent to control browning and microbes in dried fruit, some vegetables, wine and other foods, and it is also used in water treatment and photography.

See suppliersWhat to ask for on the COA
Also known as
Sodium sulphite · Disodium sulfite · E221 · CAS 7757-83-7
Facts checked
November 2026

Forms and grades of sodium sulfite

Suppliers sell different products under the same name. Specify the one you need.

  • Anhydrous powder

    Water-free powder with the most sulfite per kilogram; the most common food form.

  • Heptahydrate

    Crystals with seven molecules of water, less stable in air and lower in active content.

  • Food grade (FCC)

    Material tested to the Food Chemicals Codex for food use, separate from technical grades.

What to check on the COA

Compare each result with your own specification when the lot arrives.

Assay (iodometric titration)
Sodium sulfite content, which falls as the salt oxidizes to sulfate.
Sulfate and thiosulfate
Oxidation and process byproducts.
Selenium
A Food Chemicals Codex limit for sulfites.
Iron
Iron content, a common impurity.
Heavy metals
Lead, arsenic and other metals by ICP-MS or ICP-OES against the supplier's specification or the Food Chemicals Codex (FCC) limits.

Storage, lots and expiry

Storage and shelf life

Store sodium sulfite in tightly sealed containers in a cool, dry place, since it reacts with air and moisture and slowly oxidizes to sodium sulfate. Keep it away from acids, which release sulfur dioxide gas. Shelf life is set by the supplier's specification, and older stock is re-titrated before use.

Lots and expiry dates

Record the assay of each lot, since active sulfite content drops with age and exposure. Log additions per batch so total sulfite in finished products can be tracked for labeling.

Regulatory status

Facts from regulators and standards bodies, each linked to its source.

  • 21 CFR 182.3798 lists sodium sulfite as GRAS when used in accordance with good manufacturing practice, except that it is not used in meats, in foods recognized as a source of vitamin B1, or on fruits or vegetables served or sold raw or presented as fresh.

    Source: ecfr.gov (opens in a new tab)

  • Under 21 CFR 101.100(a)(4), a sulfiting agent such as sodium sulfite is detectable, and so cannot be treated as an insignificant incidental additive, at 10 ppm or more in the finished food.

    Source: ecfr.gov (opens in a new tab)

  • Health Canada's List of Permitted Preservatives includes sodium sulphite.

    Source: canada.ca (opens in a new tab)

This is general information, not regulatory advice. Status differs by country and by how the ingredient is used, so check the rules for your product and market.

Sodium sulfite suppliers

Manufacturers and distributors whose own websites say they sell it.

We are checking sodium sulfite suppliers now

Every listing is checked against the supplier’s own website before it goes live, so this list fills in over the coming weeks. The specs and COA checklist above are ready today.

Sell sodium sulfite? Request a listing

Frequently asked questions

What forms of sodium sulfite can brands buy?

Common forms include anhydrous powder, heptahydrate and food grade (FCC). Ask each supplier for the specification sheet of the exact grade they quote.

What should the COA for sodium sulfite include?

Expect assay (iodometric titration), sulfate and thiosulfate, selenium, iron and heavy metals, each with its method, specification and result for that lot.

How should sodium sulfite be stored?

Store sodium sulfite in tightly sealed containers in a cool, dry place, since it reacts with air and moisture and slowly oxidizes to sodium sulfate. Keep it away from acids, which release sulfur dioxide gas. Shelf life is set by the supplier's specification, and older stock is re-titrated before use.

What is the regulatory status of sodium sulfite?

21 CFR 182.3798 lists sodium sulfite as GRAS when used in accordance with good manufacturing practice, except that it is not used in meats, in foods recognized as a source of vitamin B1, or on fruits or vegetables served or sold raw or presented as fresh. Under 21 CFR 101.100(a)(4), a sulfiting agent such as sodium sulfite is detectable, and so cannot be treated as an insignificant incidental additive, at 10 ppm or more in the finished food. Health Canada's List of Permitted Preservatives includes sodium sulphite.

More acids, preservatives and leavening

All 72 acids, preservatives and leavening

Sell ingredients to brands?

Request a free listing for the ingredients you make or distribute. No paid placement.

Request a listing