Sodium metabisulfite (CAS 7681-57-4, food additive E223) is one of the most widely used preservatives and antioxidants in the food industry. From wine to dried fruit, it protects color and freshness by releasing sulfur dioxide — but its use is tightly regulated because of sulfite sensitivity. This guide covers how sodium metabisulfite is used in food, the sulfite limits, and the safety requirements.
1. How Sodium Metabisulfite Works in Food
When dissolved in food, sodium metabisulfite releases sulfur dioxide (SO2), which acts as:
- Antimicrobial: inhibits spoilage bacteria, yeasts and molds.
- Antioxidant: prevents oxidative browning and rancidity.
- Enzyme inhibitor: blocks browning enzymes (polyphenol oxidase) in fresh produce.
- Bleaching agent: lightens color in some processed foods.
This combination makes it valuable in a wide range of products — and the same SO2 chemistry is why limits and labeling are mandatory.
2. Typical Applications
| Application | Typical use |
|---|---|
| Wine and cider | Antioxidant and antimicrobial during and after fermentation |
| Dried fruit | Preserves color (apricots, raisins) and prevents spoilage |
| Juices and soft drinks | Antioxidant and preservative |
| Pickles and vegetables | Preservative and crispness retention |
| Seafood | Bleaching/antioxidant on some shrimp products |
| Potato products | Prevents browning |
3. Sulfite Limits and Regulations
Because a minority of consumers (notably some asthmatics) are sensitive to sulfites, regulators worldwide control both the permitted dose and the labeling:
- Maximum residue limits are set per food category (expressed as SO2), e.g. typically 10-2000 ppm depending on the product.
- Labeling: when the sulfite level exceeds a threshold (e.g. 10 ppm in the EU/US), the label must declare “contains sulfites”.
- Food-grade specification: sodium metabisulfite for food use must meet purity and heavy-metal limits, with the COA showing these values.
Regulations differ by country — always confirm the limits for your target market and product category.
4. Food-Grade vs Technical Grade
| Aspect | Food grade (E223) | Technical grade |
|---|---|---|
| Assay | High (e.g. 96%+ on SO2 basis) | High |
| Heavy metals | Strict limits (As, Pb, Hg…) | Less strict |
| Certification | Food-additive compliance | Not for food use |
| Use | Food, beverage | Water, textile, industrial |
Never substitute technical grade in food applications — the COA and certification must be food-grade.
5. FAQ
Is sodium metabisulfite safe in food?
Yes, when used within the permitted limits (E223) and labeled correctly. Sulfite-sensitive individuals must be informed via labeling.
Why are sulfites restricted?
Some people (especially asthmatics) are sensitive to sulfites; regulators set limits and labeling requirements to protect them.
What is the difference between E223 and sodium sulfite?
E223 is sodium metabisulfite; sodium sulfite (E221) is a different salt. Metabisulfite releases more SO2 and is the more common commercial preservative.
How should food-grade metabisulfite be stored?
Sealed, cool, dry; moisture degrades it and releases SO2. Use FIFO and check the COA batch.
6. References and Further Reading
- Food additive regulations for sulfites (E223) in your market
- Industry literature on sulfite preservation and labeling
This article is published for industrial and technical reference by PolyblueChem. Always verify regulatory limits for your market.
PolyblueChem supplies sodium metabisulfite (CAS 7681-57-4) in food and technical grades with COA and MSDS. See our sodium metabisulfite guide. Contact us for specifications and quotations.