Sodium Metabisulfite Food Grade: The Complete Guide for Winemakers, Food Processors & Industrial Users
Winemakers, food processors and water-treatment operators all use the same compound; what changes between them is the grade and the dose.
Alliance Chemical supplies sodium metabisulfite in Food Grade, ACS Reagent Grade, and Technical Grade. Need the Certificate of Analysis? Just ask, we send it at no charge. This guide covers the chemistry, the dosing, the regulations and the safety data.
What Is Sodium Metabisulfite?
Sodium metabisulfite is an inorganic compound with the formula Na₂S₂O₅ and a molecular weight of 190.10 g/mol. It appears as a white to yellowish crystalline powder with a strong sulfur dioxide odor. When dissolved in water, it releases SO₂ gas, which is the active agent responsible for most of its functional properties.
| Property | Value |
|---|---|
| Chemical Formula | Na₂S₂O₅ |
| CAS Number | 7681-57-4 |
| Molecular Weight | 190.10 g/mol |
| Appearance | White crystalline powder |
| Odor | Strong SO₂ (sulfur dioxide) |
| Solubility in Water | ~540 g/L at 20°C |
| pH (10% solution) | 4.0–5.5 |
| SO₂ Content | ~65% available SO₂ by weight |
| Decomposition Temp | ~150°C (302°F) |
| Other Names | Sodium pyrosulfite, sodium disulfite, disodium metabisulfite, E 223 |
What is the pH of sodium metabisulfite?
A 10% solution of sodium metabisulfite has a pH of 4.0 to 5.5. That range is written into the EU purity specification for food additive E 223 (Regulation (EU) No 231/2012), which also requires at least 95% Na₂S₂O₅ and at least 64% SO₂. The solution is acidic because the dissolved salt forms bisulfite ions, and it gives off SO₂ faster as the pH drops further.
What is another name for sodium metabisulfite?
Sodium metabisulfite is also sold as sodium pyrosulfite, sodium disulfite and disodium metabisulfite; EU food labels list it as E 223, and it is one of the ingredients labels group under "sulfites". All of these names mean the same compound, Na₂S₂O₅, CAS 7681-57-4. Industrial buyers often shorten it to SMBS.
Is sodium metabisulfite the same as salt?
No. Table salt is sodium chloride (NaCl). Sodium metabisulfite (Na₂S₂O₅) is a "salt" only in the chemistry sense: an ionic compound of sodium and the metabisulfite ion (S₂O₅²⁻). It does not behave like table salt: it smells of sulfur dioxide, and in water it forms acidic bisulfite, not a neutral brine.
Sodium metabisulfite vs sodium bisulfite vs sodium sulfite
Sodium metabisulfite is the dry, dehydrated form of sodium bisulfite: in water it reacts to give two bisulfite ions (Na₂S₂O₅ + H₂O → 2 NaHSO₃), so both deliver the same active chemistry. The practical differences are form and strength. By formula, metabisulfite carries 67.4% SO₂ by weight, bisulfite 61.6%, sodium sulfite 50.8% and potassium metabisulfite 57.6%.
| Compound | Formula | CAS | Molar mass | SO₂ by formula | EU food number |
|---|---|---|---|---|---|
| Sodium metabisulfite | Na₂S₂O₅ | 7681-57-4 | 190.11 g/mol | 67.4% | E 223 |
| Sodium bisulfite | NaHSO₃ | 7631-90-5 | 104.06 g/mol | 61.6% | E 222 |
| Sodium sulfite | Na₂SO₃ | 7757-83-7 | 126.05 g/mol | 50.8% | E 221 |
| Potassium metabisulfite | K₂S₂O₅ | 16731-55-8 | 222.33 g/mol | 57.6% | E 224 |
The "SO₂ by formula" column is the theoretical maximum, calculated from molar mass. Commercial material is lower: the EU E 223 specification sets a floor of 64% SO₂ for sodium metabisulfite. In the US, FDA lists all four as GRAS sulfiting agents with the same restrictions (21 CFR 182.3739, 182.3766, 182.3798 and 182.3637).
Grade Comparison: Food vs. ACS vs. Technical
Choosing the correct grade of sodium metabisulfite is critical. Using a technical-grade product in food contact applications introduces unnecessary risk, while using ACS-grade material for industrial dechlorination wastes budget. Here's how the three grades compare:
| Specification | Food Grade | ACS Reagent Grade | Technical Grade |
|---|---|---|---|
| Purity (Na₂S₂O₅) | ≥ 97.0% | ≥ 97.0% (meets ACS specs) | ≥ 95.0% |
| Iron (Fe) | ≤ 10 ppm | ≤ 5 ppm | ≤ 20 ppm |
| Heavy Metals (as Pb) | ≤ 10 ppm | ≤ 5 ppm | Not specified |
| Arsenic (As) | ≤ 3 ppm | ≤ 2 ppm | Not specified |
| Selenium (Se) | ≤ 5 ppm | ≤ 5 ppm | Not specified |
| Chloride (Cl) | Controlled | ≤ 0.02% | Not specified |
| COA Provided | Yes | Yes | Yes |
| Typical Use | Wine, food, brewing | Lab analysis, research | Water treatment, industrial |
Winemaking & Brewing: SO₂ Management Made Simple
Sodium metabisulfite is the go-to sulfite source for winemakers worldwide. It supplies the SO₂ that protects wine from oxidation during fermentation, aging, and bottling. Understanding free SO₂ targets and dosing rates is essential for producing consistent, high-quality wine.
How SO₂ Works in Wine
When sodium metabisulfite dissolves in wine (an acidic medium), it releases sulfur dioxide. The SO₂ exists in equilibrium between three forms: molecular SO₂ (the most active form), bisulfite ion (HSO₃⁻), and sulfite ion (SO₃²⁻). At typical wine pH levels (3.0–3.8), the bisulfite ion dominates, while molecular SO₂, the most chemically active fraction, is a function of both pH and free SO₂ concentration.
| Stage | Target Free SO₂ (mg/L) | Dosing Rate (Na₂S₂O₅) | Notes |
|---|---|---|---|
| Crush / Must | 25–50 mg/L | ~170–330 mg per gallon | Add before yeast pitch; adjust for fruit condition |
| Post-Fermentation | 25–35 mg/L | ~170–230 mg per gallon | Rack off lees first; test before adding |
| Aging / Racking | 20–35 mg/L | ~130–230 mg per gallon | Test and adjust at each racking |
| Pre-Bottling | 25–40 mg/L (white) 20–30 mg/L (red) |
Varies — test first | Final adjustment; measure precisely |
The dosing column uses the rule of thumb in the next section (1 g per gallon adds about 150 mg/L SO₂), so each 1 mg/L of SO₂ you need costs about 6.7 mg of sodium metabisulfite per gallon.
Quick Dosing Reference
A common rule of thumb: 1 gram of sodium metabisulfite dissolved in 1 gallon of wine adds approximately 150 mg/L of SO₂. This makes it easy to scale calculations:
| Volume | To Add ~30 mg/L SO₂ | To Add ~50 mg/L SO₂ |
|---|---|---|
| 1 Gallon (3.8 L) | ~0.20 g | ~0.33 g |
| 5 Gallons (19 L) | ~1.0 g | ~1.65 g |
| 6 Gallons (23 L) | ~1.2 g | ~2.0 g |
| 15 Gallons (57 L) | ~3.0 g | ~5.0 g |
| 60 Gallons (1 barrel) | ~12.0 g | ~20.0 g |
What are the food preservation and processing applications of sodium metabisulfite?
In food, sodium metabisulfite (E 223) is a sulfiting agent added to slow browning and oxidation in dried fruit, shrimp, wine, juices and corn starch processing. FDA lists it as GRAS except in meats, in foods that are a source of vitamin B1, and on fruits or vegetables served or sold raw (21 CFR 182.3766). Its ability to release SO₂ in solution makes it effective at slowing enzymatic and non-enzymatic browning reactions in fruits, vegetables, and seafood.
🍎 Dried Fruits
Used as a pre-treatment dip or sulfur fumigation alternative. Helps dried apricots, raisins, and apple rings maintain their natural color during dehydration and long-term storage. Typical concentrations range from 500–2,000 ppm SO₂ in the dip solution depending on the fruit and target residual level.
🥔 Fresh-Cut Produce
Not permitted in the US on fruits or vegetables intended to be served or sold raw, or presented to consumers as fresh (21 CFR 182.3766; the restriction dates to 1986). Fresh-cut apples and salad greens use sulfite-free anti-browning dips such as ascorbic acid instead. Sulfites slow browning by blocking polyphenol oxidase (PPO), which is why they remain in use on produce that is dried, cooked or processed.
🦐 Shrimp & Seafood
Used to prevent melanosis (black spot) in shrimp and crustaceans during iced storage and transportation. Applied as a dip at 1.0–1.25% sodium metabisulfite solution immediately post-harvest. This is one of the most established uses in the seafood industry.
🧃 Juice & Beverage
Functions as an antioxidant in fruit juices, cordials, and soft drinks to prevent browning and flavor degradation. Also used to maintain color in maraschino cherries, fruit toppings, and cocktail mixes. Dosing varies by product and target shelf life.
🌾 Starches & Flour
Used in corn wet milling as a steeping agent, where SO₂ helps soften kernels during the steeping process. Also applied in modified starch production where reducing conditions are required.
🍬 Sugar Refining
Employed in sugar refining as a bleaching and reducing agent to improve the whiteness and purity of the final product. The SO₂ released by metabisulfite reacts with color-forming compounds during the clarification process.
How is sodium metabisulfite used in water treatment and dechlorination?
Sodium metabisulfite is widely used in municipal and industrial water treatment for dechlorination — the removal of residual chlorine and chloramine from treated water. This is critical in applications ranging from aquaculture systems and dialysis water preparation to industrial process water and wastewater discharge compliance.
Dechlorination Chemistry
The reactions are straightforward:
| Reaction | Stoichiometry |
|---|---|
| Chlorine removal: Na₂S₂O₅ + 2Cl₂ + 3H₂O → 2NaHSO₄ + 4HCl | 1.34 mg SMBS per 1 mg Cl₂ |
| Chloramine removal: Na₂S₂O₅ + 2NH₂Cl + 3H₂O → 2NaHSO₄ + 2NH₄Cl | 1.34 mg SMBS per 1 mg chloramine measured as Cl₂ (1.85 mg per mg NH₂Cl) |
Industrial Water Applications
| Application | Typical Dosing | Key Consideration |
|---|---|---|
| RO Membrane Protection | 1.5–3.0 mg/L | Prevents chlorine damage to polyamide membranes |
| Boiler Feedwater (O₂ scavenging) | 5–10 mg/L | Reduces dissolved oxygen to prevent corrosion |
| Wastewater Discharge | Varies by permit | Removes residual chlorine to meet NPDES limits |
| Aquaculture Systems | 1.34 × residual Cl₂ | Must achieve zero chlorine before stocking |
| Dialysis Water Prep | Per facility protocol | Extremely tight tolerances; test continuously |
What are the photography and darkroom applications of sodium metabisulfite?
Sodium metabisulfite has a long history in photographic processing, where it serves as a preservative and acidifying agent in stop baths and fixer solutions. Its ability to maintain acidic conditions and scavenge oxidants makes it valuable across both black-and-white and color processing workflows.
🛑 Stop Baths
Used in acidic stop baths to immediately halt the action of alkaline developers. A 2–3% solution of sodium metabisulfite in water provides an effective stop bath that is less irritating than acetic acid-based alternatives, with the added benefit of preserving the stop bath's acidity over multiple uses.
📸 Fixer Preservative
Added to sodium thiosulfate (hypo) fixer solutions as a preservative. The SO₂ released prevents oxidation of the thiosulfate, extending the working life of the fixer. Typical addition: 15–25 g per liter of working fixer solution.
🧪 Clearing Baths
Incorporated into hypo clearing agents and wash aids to accelerate the removal of residual fixer from prints and film. Helps reduce wash times significantly while improving archival permanence of the final print.
What are the additional industrial applications of sodium metabisulfite?
⛏️ Mining & Mineral Processing
Used as a depressant in froth flotation to selectively separate sulfide minerals. Also employed in gold processing as a reducing agent and in heap leach operations for cyanide detoxification.
🧵 Textile & Pulp
Applied as a bleaching agent and antichlor in textile processing. In the pulp and paper industry, used to remove residual chlorine from bleaching stages and as a reducing agent in brightening formulations.
🧴 Cosmetics & Personal Care
Functions as an antioxidant preservative in cosmetic formulations. Helps prevent oxidation of active ingredients and color changes in creams, lotions, and hair care products. Used at low concentrations per formulation guidelines.
What are the safety, handling, and storage guidelines for sodium metabisulfite?
Personal Protective Equipment (PPE)
| PPE Item | Recommendation |
|---|---|
| Eye Protection | Chemical splash goggles or safety glasses with side shields |
| Skin Protection | Chemical-resistant gloves (nitrile or rubber); long sleeves |
| Respiratory | NIOSH-approved respirator if dust or SO₂ is generated; work in well-ventilated area |
| General | Avoid inhaling dust; wash hands thoroughly after handling |
Storage Conditions
- Container: Keep in original, tightly sealed container. Use HDPE, polypropylene, or glass. Avoid metal containers, as SO₂ can corrode metals.
- Environment: Store in a cool, dry, well-ventilated area away from direct sunlight and heat sources.
- Incompatibles: Keep away from strong acids (releases large amounts of SO₂), strong oxidizers, and moisture. Do not store with bases or bleach.
- Shelf Life: Properly stored, sodium metabisulfite maintains its rated purity for 12–24 months. Over time, exposure to moisture and air causes slow decomposition to sodium sulfate, reducing effective SO₂ content.
- Spill Response: Sweep up dry material carefully to minimize dust. Avoid washing into drains. Dispose of in accordance with local regulations.
Is sodium metabisulfite safe?
In food, FDA lists sodium metabisulfite as generally recognized as safe at good manufacturing practice levels, except in meats, vitamin B1 source foods and raw produce, and any food with 10 ppm or more must declare sulfites on the label. As a bulk powder it is a hazardous chemical: GHS signal word Danger, H302 (harmful if swallowed) and H318 (causes serious eye damage).
| Measure | Value | Source |
|---|---|---|
| GHS classification (EU CLP harmonized) | Danger; H302, H318 | PubChem (Regulation (EC) 1272/2008) |
| NIOSH REL | 5 mg/m³, 10-hour TWA | NIOSH Pocket Guide |
| OSHA PEL | None established | NIOSH Pocket Guide |
| IDLH | Not determined | NIOSH Pocket Guide |
| US food labeling trigger | 10 ppm or more sulfite in the finished food | 21 CFR 101.100(a)(4) |
| US wine labeling trigger | 10 ppm or more SO₂ or sulfiting agent: "Contains sulfites" | 27 CFR 4.32(e) |
The practical hazard at work is the dust and the SO₂ it gives off: both irritate the eyes and airways, and acids release SO₂ quickly. Some people are sensitive to sulfites, particularly some people with asthma, which is why US and EU rules require the sulfite declaration. In 2022 the European Food Safety Authority withdrew its temporary acceptable daily intake of 0.7 mg SO₂ equivalents per kg body weight per day and reported that estimated intakes for high consumers raise a safety concern (EFSA Journal 2022;20(11):7594). For handling, read the SDS; for questions about your own health, ask a physician.
Is sodium metabisulfite banned in Europe?
No. Sodium metabisulfite is an authorized EU food additive, E 223, under Annexes II and III of Regulation (EC) No 1333/2008. Each permitted food category has a maximum level expressed as SO₂ from all sources, and any food or drink above 10 mg/kg or 10 mg/L total SO₂ must declare "sulphites" as an allergen under Regulation (EU) No 1169/2011.
What changed in Europe is the safety review, not the authorization. EFSA's 2022 follow-up (above) replaced the temporary ADI with a margin-of-exposure approach and recommended lower EU limits for arsenic, lead and mercury in the additive, plus a new cadmium limit. The current EU purity specification for E 223 (Regulation (EU) No 231/2012) sets arsenic at 3 mg/kg, lead at 2 mg/kg and mercury at 1 mg/kg maximum.
What can I use instead of sodium metabisulfite?
The substitute depends on the job. In wine, potassium metabisulfite does the same thing without adding sodium. For dechlorination, sodium bisulfite, sodium sulfite, sodium thiosulfate, sulfur dioxide and activated carbon are the standard alternatives. To stop browning on fresh-cut produce, where sulfites are not allowed, processors use ascorbic acid or citric acid.
| Job | Alternative | What to know |
|---|---|---|
| Wine and cider SO₂ additions | Potassium metabisulfite (E 224) | 57.6% SO₂ by formula vs 67.4%, so about 17% more by weight for the same addition |
| Dechlorination | Sodium bisulfite solution, sodium sulfite, sodium thiosulfate, SO₂ gas, carbon adsorption | All listed by US EPA (fact sheet 832-F-00-022); see our sodium thiosulfate guide |
| Anti-browning on fresh-cut fruit | Ascorbic acid, citric acid | Both GRAS (21 CFR 182.3013, 21 CFR 184.1033); no sulfite label declaration |
| Photographic stop bath | Acetic acid stop bath | The traditional choice; metabisulfite is the less irritating option |
What packaging and sizing options are available for sodium metabisulfite?
Alliance Chemical offers sodium metabisulfite in 2 lb, 5 lb and 50 lb bags, with multi-packs and multi-bag lots up to forty 50 lb bags, from home winemakers processing a few gallons to food manufacturers running continuous production lines.
| Size | Best For | Typical Users |
|---|---|---|
| 2 lb bag (packs of 1 to 16) | Small batches, homebrewing, testing | Home winemakers, hobbyist photographers, small labs |
| 5 lb bag (packs of 1 to 4) | Regular use, small production runs | Craft wineries, small food processors, school labs |
| 50 lb bag | Medium-volume operations | Regional wineries, water treatment operators, commercial kitchens |
| 10, 20 or 40 × 50 lb bags | High-volume continuous use | Large wineries, food manufacturers, industrial plants, water systems |
Ready to Order Sodium Metabisulfite?
Alliance Chemical stocks Food Grade, ACS Reagent Grade, and Technical Grade sodium metabisulfite in 2 lb, 5 lb and 50 lb bags, up to forty-bag lots. Need the Certificate of Analysis? Just ask, we send it at no charge.
Related Reading
📘 Engineer's Guide to Sodium Bisulfite for Dechlorination
Deep dive into stoichiometry, dosing calculations, and system design for chlorine removal. Read the guide →
💧 Ultimate Guide to Water Treatment Chemicals
Comprehensive overview of chemicals used in potable, industrial, and wastewater treatment. Read the guide →
🏭 Pro Guide to Chemical Storage
Best practices for storing chemicals — from small lab quantities to bulk industrial inventory. Read the guide →
📋 How to Read a Chemical COA
Understand what every line on your Certificate of Analysis means and how to verify quality. Read the guide →
🔬 Understanding Chemical Grades
ACS, food grade, technical, USP — learn what each grade means and when each one matters. Read the guide →
Frequently Asked Questions
What is the difference between sodium metabisulfite and sodium bisulfite?
Sodium metabisulfite (Na₂S₂O₅) and sodium bisulfite (NaHSO₃) are closely related compounds that both release SO₂ in solution. The key practical difference is concentration: metabisulfite delivers approximately 65% available SO₂ by weight versus about 61% for bisulfite. Metabisulfite is also available as a stable dry powder, while bisulfite is typically supplied as a liquid solution (typically 38–40% concentration). For most applications, they can be used interchangeably with appropriate dosing adjustments.
How much sodium metabisulfite do I add to wine?
The amount depends on your target free SO₂ level, current SO₂ levels, and wine pH. As a general starting point, 1 gram of sodium metabisulfite per gallon of wine adds approximately 150 mg/L of SO₂. Most winemakers target 25–50 mg/L free SO₂ at crush and 20–40 mg/L at bottling. Always measure your wine's current free SO₂ level with a reliable test before adding. Wines with higher pH require more total SO₂ to achieve adequate molecular SO₂ levels.
Can sodium metabisulfite be used to remove chloramine from tap water?
Yes. Sodium metabisulfite reacts rapidly with both chlorine and chloramine in water. The stoichiometric ratio is approximately 1.34 mg of sodium metabisulfite per 1 mg of chlorine, or of chloramine measured as Cl₂. In practice, a slight excess (1.5:1 to 2.0:1) is used to ensure complete removal. For homebrewing water preparation, one Campden tablet (approximately 0.44 g of sodium metabisulfite) can treat about 20 gallons of water.
How should I store sodium metabisulfite to maintain its potency?
Store in a tightly sealed container in a cool, dry, well-ventilated area away from direct sunlight, heat, moisture, strong acids, and strong oxidizers. Use HDPE, polypropylene, or glass containers — avoid metal, which can corrode from SO₂ exposure. When stored properly, the powder maintains its rated purity for 12–24 months. Once opened, use within 6 months or transfer to an airtight container to minimize moisture absorption and SO₂ loss.
What PPE do I need when handling sodium metabisulfite?
At minimum, wear chemical splash goggles and chemical-resistant gloves (nitrile or rubber). Work in a well-ventilated area, as the powder and its solutions release SO₂ gas, which irritates the respiratory system. If you're generating dust (such as when weighing or transferring large quantities), use a NIOSH-approved respirator with acid gas/P100 cartridges. Avoid inhaling dust and wash hands thoroughly after handling. Always consult the SDS for complete safety information.
Is sodium metabisulfite the same as potassium metabisulfite?
They are very similar in function. Both release SO₂ in solution and are used interchangeably in many applications, including winemaking. The primary difference is the cation: sodium (Na⁺) versus potassium (K⁺). Some winemakers prefer potassium metabisulfite because it does not contribute sodium to the wine. However, sodium metabisulfite is more soluble and often less expensive at industrial scale. From a dosing perspective, potassium metabisulfite has a molecular weight of 222.32 g/mol versus 190.10 g/mol for the sodium form, so dosing rates differ slightly.
What food grade certifications does Alliance Chemical's sodium metabisulfite meet?
Alliance Chemical's food grade sodium metabisulfite is supplied to Food Chemicals Codex (FCC) specifications for purity, heavy metals and impurity limits. Need the Certificate of Analysis? Just ask, we send it at no charge. It documents the purity, iron, heavy metals, arsenic and other parameters for your lot. For questions about specific certifications, contact our team directly.
Shop sodium metabisulfite by grade: Food Grade, ACS Grade, or Technical Grade.
Related: What Phosphoric Acid Actually Does in Food — the same grade-selection logic applied to phosphoric acid.
References & Authoritative Sources
Primary sources consulted for this article. Regulatory and physical-property figures above are drawn from these references.
- Sodium metabisulfite (CAS 7681-57-4) — compound summary — PubChem, National Center for Biotechnology Information. Accessed 2026-09-01.
- 21 CFR 182.3766 — Sodium metabisulfite (chemical preservatives generally recognized as safe) — Electronic Code of Federal Regulations, U.S. Food and Drug Administration. Accessed 2026-09-01.
- 21 CFR 101.100 — Food labeling exemptions; sulfiting agents at 10 ppm or more must be declared — Electronic Code of Federal Regulations, U.S. Food and Drug Administration. Accessed 2026-09-01.
- 27 CFR 4.32 — Mandatory label information for wine, including the sulfite declaration — Electronic Code of Federal Regulations, Alcohol and Tobacco Tax and Trade Bureau. Accessed 2026-09-01.
- NIOSH Pocket Guide to Chemical Hazards: Sodium metabisulfite, Centers for Disease Control and Prevention. Accessed 2026-09-26.
- Commission Regulation (EU) No 231/2012, specifications for food additives (E 223 sodium metabisulphite), EUR-Lex. Accessed 2026-09-26.
- EFSA FAF Panel (2022), Follow-up of the re-evaluation of sulfur dioxide (E 220) and sulfites (E 221 to E 228), EFSA Journal 20(11):7594. Accessed 2026-09-26.
- Wastewater Technology Fact Sheet: Dechlorination (EPA 832-F-00-022), U.S. Environmental Protection Agency. Accessed 2026-09-26.
Key numbers and sources
| Fact | Value | Source |
|---|---|---|
| CAS number | 7681-57-4 | pubchem.ncbi.nlm.nih.gov |
| Chemical formula | Na₂S₂O₅ | pubchem.ncbi.nlm.nih.gov |
| Molecular weight | 190.10 g/mol | pubchem.ncbi.nlm.nih.gov |
| Solubility in water at 20°C | ~540 g/L at 20°C | pubchem.ncbi.nlm.nih.gov |
| pH (10% solution) | 4.0–5.5 | Regulation (EU) No 231/2012 (E 223 specification) |
| SO₂ content by weight | ~65% available SO₂ by weight | See article text |
| Sulfite labeling threshold in food | 10 ppm or more total SO₂ | ecfr.gov |
| NIOSH REL (TWA) | 5 mg/m³; no OSHA PEL | cdc.gov/niosh |
| EU E 223 minimum assay | 95% Na₂S₂O₅, 64% SO₂ | Regulation (EU) No 231/2012 (E 223 specification) |
Frequently asked questions
Is sodium metabisulfite safe?
In food, FDA lists sodium metabisulfite as generally recognized as safe (21 CFR 182.3766) except in meats, foods that are a source of vitamin B1, and fruits or vegetables served or sold raw; foods with 10 ppm or more must declare sulfites. As a bulk powder it is hazardous: GHS Danger, H302 harmful if swallowed and H318 causes serious eye damage. NIOSH recommends a 5 mg/m³ limit (10-hour TWA); OSHA has no PEL. Some people, particularly some with asthma, are sensitive to sulfites. Read the SDS before handling.
Is sodium metabisulfite banned in Europe?
No. Sodium metabisulfite is an authorized EU food additive, E 223, under Annexes II and III of Regulation (EC) No 1333/2008, with maximum levels per food category expressed as SO₂. Foods above 10 mg/kg or 10 mg/L total SO₂ must declare sulphites as an allergen. In 2022 EFSA withdrew its temporary acceptable daily intake of 0.7 mg SO₂ equivalents per kg body weight and flagged a safety concern for high consumers, but the additive remains authorized.
What is another name for sodium metabisulfite?
Sodium metabisulfite is also called sodium pyrosulfite, sodium disulfite and disodium metabisulfite. On EU food labels it is E 223, and ingredient lists often group it under "sulfites". Industrial buyers shorten it to SMBS. Every one of these names refers to the same compound, Na₂S₂O₅, CAS 7681-57-4, a white crystalline powder that smells of sulfur dioxide.
Is sodium metabisulfite the same as salt?
No. Table salt is sodium chloride, NaCl. Sodium metabisulfite, Na₂S₂O₅, is a salt only in the chemistry sense: an ionic compound of sodium and the metabisulfite ion. It smells of sulfur dioxide, and in water it forms acidic bisulfite (a 10% solution is pH 4.0 to 5.5) instead of a neutral brine. It is used as a preservative and reducing agent, not as a seasoning.
What is the difference between sodium metabisulfite and sodium bisulfite?
Sodium metabisulfite (Na₂S₂O₅) is the dry, dehydrated form of sodium bisulfite (NaHSO₃): dissolved in water it becomes bisulfite, so both deliver the same chemistry. Metabisulfite carries more SO₂ per gram, 67.4% by formula versus 61.6% for bisulfite, and ships as a stable powder, while bisulfite is usually sold as a liquid solution of about 38 to 40%. With a dose adjustment they are interchangeable in most uses.
What can I use instead of sodium metabisulfite?
It depends on the job. In wine, potassium metabisulfite does the same thing without adding sodium, at about 17% more by weight. For dechlorination, US EPA lists sodium bisulfite, sodium sulfite, sodium thiosulfate, sulfur dioxide and carbon adsorption as alternatives. To keep fresh-cut fruit from browning, where sulfites are not allowed in the US, processors use ascorbic acid or citric acid.
How much sodium metabisulfite do I add to wine?
It depends on your target free SO₂, the SO₂ already in the wine, and the wine pH. As a starting point, 1 gram of sodium metabisulfite per gallon adds about 150 mg/L of SO₂, so each 1 mg/L you need takes about 6.7 mg per gallon. Most winemakers target 25 to 50 mg/L free SO₂ at crush and 20 to 40 mg/L at bottling. Measure free SO₂ before every addition; higher pH wines need more.
Can sodium metabisulfite be used to remove chloramine from tap water?
Yes. Sodium metabisulfite reacts rapidly with both chlorine and chloramine. The stoichiometric dose is about 1.34 mg of sodium metabisulfite per 1 mg of chlorine, or of chloramine measured as Cl₂ (1.85 mg per mg of NH₂Cl). In practice a slight excess of 1.5:1 to 2.0:1 makes sure the residual is gone. For brewing water, one Campden tablet, about 0.44 g, handles roughly 20 gallons.
How should I store sodium metabisulfite to maintain its potency?
Keep it in a tightly sealed HDPE, polypropylene or glass container in a cool, dry, ventilated area away from sunlight, heat, moisture, strong acids and strong oxidizers. Avoid metal containers, which SO₂ corrodes. In moist air the powder slowly loses SO₂ and oxidizes to sodium sulfate. Stored properly it holds its rated purity for 12 to 24 months; once opened, use it within about 6 months.
What PPE do I need when handling sodium metabisulfite?
Wear chemical splash goggles, because the powder is classified H318 (causes serious eye damage), plus nitrile or rubber gloves. Work with ventilation, since the powder and its solutions give off SO₂. When weighing or transferring enough to raise dust, use a NIOSH-approved respirator with acid gas and P100 cartridges; NIOSH recommends a 5 mg/m³ limit. Wash hands after handling and consult the SDS for full details.
Is sodium metabisulfite the same as potassium metabisulfite?
They work the same way. Both release SO₂ in solution and are used interchangeably in winemaking. The difference is the cation: sodium versus potassium. Some winemakers prefer potassium metabisulfite because it adds no sodium to the wine. Potassium metabisulfite has a molar mass of 222.33 g/mol versus 190.11 g/mol for the sodium salt, so it carries 57.6% SO₂ by formula against 67.4%, and you need about 17% more of it.
What food grade certifications does Alliance Chemical's sodium metabisulfite meet?
Alliance Chemical's food grade sodium metabisulfite is supplied to Food Chemicals Codex (FCC) specifications for purity, heavy metals and impurity limits. Need the Certificate of Analysis? Just ask, we send it at no charge. It documents the purity, iron, heavy metals, arsenic and other parameters for your lot. For questions about a specific certification your process requires, contact our team before you order.
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About the author
Andre Taki
This article is for informational purposes only.
