Sodium Metabisulfite Food Grade: The Complete Guide
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Find quick answers to common questions about sodium metabisulfite food grade: the complete guide.
Sodium Metabisulfite Food Grade: The Complete Guide for Winemakers, Food Processors & Industrial Users
Sodium metabisulfite (Na₂S₂O₅) is one of the most versatile sulfite compounds used across the food, beverage, water treatment, and photography industries. As a potent source of sulfur dioxide (SO₂), this white crystalline powder serves critical roles as an antioxidant, preservative, and reducing agent. Whether you're a winemaker managing sulfite levels, a food processor extending shelf life, or an industrial operator treating process water, understanding how to select the right grade and apply proper dosing is essential.
Alliance Chemical supplies sodium metabisulfite in Food Grade, ACS Reagent Grade, and Technical Grade — with every order backed by a Certificate of Analysis (COA) and Safety Data Sheet (SDS). This guide covers everything you need to know to work with this compound confidently and effectively.
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) | 3.5–5.0 |
| SO₂ Content | ~65% available SO₂ by weight |
| Decomposition Temp | ~150°C (302°F) |
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 protects wine from oxidation and undesirable microbial activity 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 fraction most important for microbial control — 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 | ~40–80 mg per gallon | Add before yeast pitch; adjust for fruit condition |
| Post-Fermentation | 25–35 mg/L | ~40–55 mg per gallon | Rack off lees first; test before adding |
| Aging / Racking | 20–35 mg/L | ~30–55 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 |
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 |
Food Preservation & Processing Applications
In the food industry, sodium metabisulfite functions primarily as an antioxidant and browning inhibitor. 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
Applied in anti-browning dip solutions for peeled potatoes, cut apples, and shredded lettuce. Inhibits polyphenol oxidase (PPO), the enzyme responsible for enzymatic browning. Concentrations of 100–500 ppm are typical for fresh-cut applications.
🦐 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 and inhibit microbial growth 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.
Water Treatment & 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 + 5H₂O → 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 |
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 |
Photography & Darkroom Applications
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.
Additional Industrial Applications
⛏️ 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.
Safety, Handling & Storage
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.
Packaging & Sizing Guide
Alliance Chemical offers sodium metabisulfite in a range of sizes to fit every operation — from home winemakers processing a few gallons to food manufacturers running continuous production lines.
| Size | Best For | Typical Users |
|---|---|---|
| Quart (≈ 2 lbs) | Small batches, homebrewing, testing | Home winemakers, hobbyist photographers, small labs |
| Gallon (≈ 8 lbs) | Regular use, small production runs | Craft wineries, small food processors, school labs |
| 5-Gallon Pail (≈ 40 lbs) | Medium-volume operations | Regional wineries, water treatment operators, commercial kitchens |
| 55-Gallon Drum (≈ 400 lbs) | High-volume continuous use | Large wineries, food manufacturers, industrial plants |
| 275-Gallon Tote (≈ 2,000+ lbs) | Bulk industrial supply | Municipal water systems, large-scale food processors, mining operations |
Ready to Order Sodium Metabisulfite?
Alliance Chemical stocks Food Grade, ACS Reagent Grade, and Technical Grade sodium metabisulfite in sizes from quart bottles to 275-gallon totes. Every order includes a Certificate of Analysis and Safety Data Sheet.
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 chloramine. 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 provided with your order 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 meets Food Chemical Codex (FCC) specifications for purity, heavy metals, and impurity limits. Every lot is tested and ships with a lot-specific Certificate of Analysis (COA) documenting the exact purity, iron content, heavy metals, arsenic, and other quality parameters. A Safety Data Sheet (SDS) is also included with every order. For questions about specific certifications, contact our team directly.
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 chloramine. 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 provided with your order 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 meets Food Chemical Codex (FCC) specifications for purity, heavy metals, and impurity limits. Every lot is tested and ships with a lot-specific Certificate of Analysis (COA) documenting the exact purity, iron content, heavy metals, arsenic, and other quality parameters. A Safety Data Sheet (SDS) is also included with every order. For questions about specific certifications, contact our team directly.
