Sulfurous acid

CAS 7782-99-2

Listed as a preservative and an acidity regulator by Canada.

Listed as preservatives (CA) · acidity regulators (CA)
Chemical structure of Sulfurous acid, from PubChem compound 1100
Structure from PubChem CID 1100 (National Library of Medicine, public domain). A depiction of one compound: where a listing covers a family, or a substance has no single structure, this page shows none.

Sulfurous acid is what sulfur dioxide forms in water, and it is the form in which sulphite treatment is often applied. It is a preservative and antioxidant, and a sulphite for labelling purposes.

Where it is and isn’t permitted

Status of Sulfurous acid by jurisdiction. Every jurisdiction this site covers is listed, including those where the substance does not appear.
JurisdictionStatusScope and limitsCitation
Australia and New ZealandFood Standards Australia New ZealandNo listed food uses foundThis site has not matched this substance to any food use on this jurisdiction’s list of authorised food additives. A food additive may be used only in foods that list names. Flavourings, enzymes, processing aids and added nutrients are regulated separately and do not appear on it.
CanadaHealth CanadaPermitted, with conditions

no numerical limit (good manufacturing practice)

16 permitted uses

Show every permitted use
  • In: Gelatin. Purpose: Acidity regulator. Limit: Good Manufacturing Practice. The amount not to exceed 500 ppm in the finished gelatin, calculated as sulphur dioxide. — Health Canada, List of Permitted Acidity Regulators and Acid-Reacting Materials (List 10), item S.24
  • In: Apple and (naming the fruit or fruits) jam; Concentrated (naming the fruit) juice, except frozen concentrated orange juice; Fig marmalade with pectin; Frozen sliced apples; (Naming the fruit or fruits) jam; (Naming the fruit or fruits) jam with pectin; (Naming the fruit or fruits) jelly with pectin; (Naming the fruit) juice; (Naming the fruits) juice; (Naming the citrus fruit or citrus fruits) marmalade with pectin; Mincemeat; Pickles and relishes; Pineapple marmalade with pectin; Rhubarb and (naming the fruit or fruits) jam; Tomato catsup; Tomato paste; Tomato pulp; Tomato puree. Purpose: Preservative. Limit: If used singly, the amount not to exceed 500 ppm, calculated as sulphur dioxide. If used in any combination with potassium bisulphite, potassium metabisulphite, sodium bisulphite, sodium dithionite, sodium metabisulphite or sodium sulphite, the total combined amount not to exceed 500 ppm, calculated as sulphur dioxide. — Health Canada, List of Permitted Preservatives (List 11), item S.18(a)
  • In: Beer. Purpose: Preservative. Limit: If used singly, the amount not to exceed 15 ppm, calculated as sulphur dioxide. If used in any combination with potassium bisulphite, potassium metabisulphite, sodium bisulphite, sodium dithionite, sodium metabisulphite or sodium sulphite, the total combined amount not to exceed 15 ppm, calculated as sulphur dioxide. — Health Canada, List of Permitted Preservatives (List 11), item S.18(b)
  • In: Cider; Fruit wine; Honey wine; Wine. Purpose: Preservative. Limit: Good Manufacturing Practice. The amount of sulphurous acid, added singly or in any combination with potassium bisulphite, potassium metabisulphite, sodium bisulphite, sodium dithionite, sodium metabisulphite or sodium sulphite, not to exceed 70 ppm in the free state in the finished product, calculated as sulphur dioxide, or 350 ppm in the combined state in the finished product, calculated as sulphur dioxide. — Health Canada, List of Permitted Preservatives (List 11), item S.18(c)
  • In: Crustaceans. Purpose: Preservative. Limit: Good Manufacturing Practice. May be used singly or in any combination with potassium bisulphite, potassium metabisulphite, sodium bisulphite, sodium dithionite, sodium metabisulphite or sodium sulphite. In either case, the total amount not to exceed 100 ppm in the edible portion of the uncooked food, calculated as sulphur dioxide. — Health Canada, List of Permitted Preservatives (List 11), item S.18(d)
  • In: Dextrose anhydrous; Dextrose monohydrate. Purpose: Preservative. Limit: If used singly, the amount not to exceed 20 ppm, calculated as sulphur dioxide. If used in any combination with potassium bisulphite, potassium metabisulphite, sodium bisulphite, sodium dithionite, sodium metabisulphite or sodium sulphite, the total combined amount not to exceed 20 ppm, calculated as sulphur dioxide. — Health Canada, List of Permitted Preservatives (List 11), item S.18(e)
  • In: Dried fruits and vegetables. Purpose: Preservative. Limit: If used singly, the amount not to exceed 2,500 ppm, calculated as sulphur dioxide. If used in any combination with potassium bisulphite, potassium metabisulphite, sodium bisulphite, sodium dithionite, sodium metabisulphite or sodium sulphite, the total combined amount not to exceed 2,500 ppm, calculated as sulphur dioxide. — Health Canada, List of Permitted Preservatives (List 11), item S.18(f)
  • In: Fancy molasses; Refiners' molasses; (Naming the source of the glucose) syrup; Table molasses. Purpose: Preservative. Limit: If used singly, the amount not to exceed 500 ppm, calculated as sulphur dioxide. If used in any combination with potassium bisulphite, potassium metabisulphite, sodium bisulphite, sodium dithionite, sodium metabisulphite or sodium sulphite, the total combined amount not to exceed 500 ppm, calculated as sulphur dioxide. — Health Canada, List of Permitted Preservatives (List 11), item S.18(g)
  • In: Frozen mushrooms. Purpose: Preservative. Limit: If used singly, the amount not to exceed 90 ppm, calculated as sulphur dioxide. If used in any combination with potassium bisulphite, potassium metabisulphite, sodium bisulphite, sodium dithionite, sodium metabisulphite or sodium sulphite, the total combined amount not to exceed 90 ppm, calculated as sulphur dioxide. — Health Canada, List of Permitted Preservatives (List 11), item S.18(h)
  • In: Gelatin. Purpose: Preservative. Limit: If used singly, the amount not to exceed 500 ppm, calculated as sulphur dioxide. If used in any combination with potassium bisulphite, potassium metabisulphite, sodium bisulphite, sodium dithionite, sodium metabisulphite or sodium sulphite, the total combined amount not to exceed 500 ppm, calculated as sulphur dioxide. — Health Canada, List of Permitted Preservatives (List 11), item S.18(i)
  • In: Glucose, except glucose used for the manufacture of sugar confectionery. Purpose: Preservative. Limit: If used singly, the amount not to exceed 40 ppm, calculated as sulphur dioxide. If used in any combination with potassium bisulphite, potassium metabisulphite, sodium bisulphite, sodium dithionite, sodium metabisulphite or sodium sulphite, the total combined amount not to exceed 40 ppm, calculated as sulphur dioxide. — Health Canada, List of Permitted Preservatives (List 11), item S.18(j)
  • In: Glucose solids, except glucose solids used for the manufacture of sugar confectionery. Purpose: Preservative. Limit: If used singly, the amount not to exceed 40 ppm, calculated as sulphur dioxide. If used in any combination with potassium bisulphite, potassium metabisulphite, sodium bisulphite, sodium dithionite, sodium metabisulphite or sodium sulphite, the total combined amount not to exceed 40 ppm, calculated as sulphur dioxide. — Health Canada, List of Permitted Preservatives (List 11), item S.18(k)
  • In: Glucose solids used for the manufacture of sugar confectionery. Purpose: Preservative. Limit: If used singly, the amount not to exceed 150 ppm, calculated as sulphur dioxide. If used in any combination with potassium bisulphite, potassium metabisulphite, sodium bisulphite, sodium dithionite, sodium metabisulphite or sodium sulphite, the total combined amount not to exceed 150 ppm, calculated as sulphur dioxide. — Health Canada, List of Permitted Preservatives (List 11), item S.18(l)
  • In: Glucose used for the manufacture of sugar confectionery. Purpose: Preservative. Limit: If used singly, the amount not to exceed 400 ppm, calculated as sulphur dioxide. If used in any combination with potassium bisulphite, potassium metabisulphite, sodium bisulphite, sodium dithionite, sodium metabisulphite or sodium sulphite, the total combined amount not to exceed 400 ppm, calculated as sulphur dioxide. — Health Canada, List of Permitted Preservatives (List 11), item S.18(m)
  • In: Unstandardized beverages. Purpose: Preservative. Limit: If used singly, the amount not to exceed 100 ppm, calculated as sulphur dioxide. If used in any combination with potassium bisulphite, potassium metabisulphite, sodium bisulphite, sodium dithionite, sodium metabisulphite or sodium sulphite, the total combined amount not to exceed 100 ppm, calculated as sulphur dioxide. — Health Canada, List of Permitted Preservatives (List 11), item S.18(n)
  • In: Unstandardized foods, except foods recognized as sources of thiamine, unstandardized preparations of meat or meat by-product, fish or meat (as defined in section B.21.002 of the Food and Drug Regulations), or poultry meat or poultry meat by-product and unstandardized foods set out in paragraphs (f) and (n) of this item. Purpose: Preservative. Limit: If used singly, the amount not to exceed 500 ppm, calculated as sulphur dioxide. If used in any combination with potassium bisulphite, potassium metabisulphite, sodium bisulphite, sodium dithionite, sodium metabisulphite or sodium sulphite, the total combined amount not to exceed 500 ppm, calculated as sulphur dioxide. Amendment notices: NOM/ADM-0122. — Health Canada, List of Permitted Preservatives (List 11), item S.18(o)
Health Canadaand 15 further provisionsretrieved 2026-10-17
European UnionEuropean Commission / EFSANo listed food uses foundThis site has not matched this substance to any food use on this jurisdiction’s list of authorised food additives. A food additive may be used only in foods that list names. Flavourings, enzymes, processing aids and added nutrients are regulated separately and do not appear on it.
Great BritainFood Standards Agency / Food Standards ScotlandNo listed food uses foundThis site has not matched this substance to any food use on this jurisdiction’s list of authorised food additives. A food additive may be used only in foods that list names. Flavourings, enzymes, processing aids and added nutrients are regulated separately and do not appear on it.
JapanConsumer Affairs AgencyNo listing matchedThis site imports only Japan’s list of designated additives (Appended Table 1 to the Regulations for Enforcement of the Food Sanitation Act), matched by English name. Existing additives, natural flavouring agents and ordinary foods used as additives are permitted outside that list and are not imported, so an empty row does not show that Japan does not permit the substance.
South KoreaMinistry of Food and Drug SafetyNo listing matchedThis site imports Part III of South Korea’s Standards and Specifications for Food Additives, matched by CAS number, then INS number, then exact name. Mixed preparations and sanitisers are not imported, and an entry whose identifiers disagreed with a page’s is held for review, so an empty row does not show that South Korea does not permit the substance.
United StatesFood and Drug AdministrationNot listedDoes not appear on this jurisdiction’s permitted list. That is not the same as being prohibited.
Codex AlimentariusCodex Alimentarius Commission / JECFANot listedDoes not appear on this jurisdiction’s permitted list. That is not the same as being prohibited.

How much is permitted

A listing usually limits the quantity as well as the food. Only one of the forms that takes is a figure: quantum satis and good manufacturing practice permit the amount the technological effect requires and no more, which is a limit rather than the absence of one. Figures below are the range across every food category this page is listed in, and categories differ between regulators — see how much is permitted.

Canada—3 GMP, 13 no quantity stated

No regulator sets a figure for Sulfurous acid. That is not an absence of control: where the listing says quantum satis or good manufacturing practice, the quantity is limited to what the effect requires.

What it is made from

Made by dissolving sulfur dioxide in water; it exists only in solution.

  • Vegan
  • Vegetarian

Compare other additives on the dietary indexes.

CAS registry number
7782-99-2
InChIKey
LSNNMFCWUKXFEE-UHFFFAOYSA-N
PubChem
CID 1100

Every name it appears under

17 recorded names. A label may use any of them.

CAS registry number

  • 7782-99-2

Other names

  • acide sulfureux
  • acido sulfuroso
  • dihydrogen trioxosulfate
  • dihydroxidooxidosulfur
  • schweflige Saeure
  • Schweflige saure
  • Sulfur dioxide 6 % solution
  • Sulfurous acid
  • SULFUROUS ACID (H2SO3)
  • SULFUROUS ACID (II)
  • Sulfurous acid, SO2 (6.0%) in water
  • SULPHUROSUM ACIDUM
  • Sulphurous Acid
  • trioxosulfuric acid
  • Trioxosulphate(2-)
  • Trioxosulphate(IV)

Hazard reference values

No reference value for this substance in the sources we hold.

Evidence and how bodies read it

Studies, and the differing conclusions regulators drew from them, are curated rather than machine-read, and none has been written for this substance yet.

Common questions

Assembled from what is above, in the words the questions are usually asked in. Each answer is the same statement the relevant section makes, with the same citations behind it.

What is Sulfurous acid?
Sulfurous acid is what sulfur dioxide forms in water, and it is the form in which sulphite treatment is often applied. It is a preservative and antioxidant, and a sulphite for labelling purposes.
What is Sulfurous acid used for in food?
It is listed as a preservative and an acidity regulator — the role Canada assigns it. This page shows every function each regulator records, with the citation for each.
Where is Sulfurous acid permitted?
Of the seven regulators this site reads, Canada permits it. Each permission is for named foods at named levels, not a blanket one; the table on this page gives them with citations.
Is Sulfurous acid vegan?
Yes. Sulfurous acid is not derived from animals, and is suitable for vegetarians. This page says what it is made from and how.

Sources for this page

  • ca retrieved 2026-10-17

Full licence terms and publisher details on Sources. How this page is built and updated: Method.

Machine-readable: a JSON record of this additive is given on request —how to ask for access.

Follow changes to Sulfurous acid:Atom feed — regulatory events, and any change the weekly refresh detects in its provisions.