What is calcium silicate and why is it in table salt?
Calcium silicate is a white, odorless, and finely powdered inorganic compound formed from calcium oxide and silica. It is primarily added to table salt as an anti-caking agent, which means it prevents the salt crystals from sticking together and forming clumps. The porous structure of calcium silicate allows it to absorb excess moisture from the air, creating a protective barrier around each salt particle. This is especially important for table salt, which is often stored in shakers and used in environments with varying humidity levels. Without this additive, the salt would absorb moisture and solidify into a hard block.
The free-flowing advantage
The presence of calcium silicate ensures that salt remains loose and easy to pour or sprinkle, which is a significant convenience for both consumers and food manufacturers. This functional property improves the product's shelf life and maintains its quality over time. Beyond table salt, calcium silicate is also used as an anti-caking agent in other powdered foods, such as:
- Spices and seasonings
- Baking powder
- Dry food mixes
- Certain powdered dairy products
Typical amounts and regulatory standards
The amount of calcium silicate in table salt is very small and is strictly regulated by food safety authorities around the world. In the United States, the Food and Drug Administration (FDA) has classified calcium silicate as “Generally Recognized as Safe” (GRAS) for use in food, provided it does not exceed 2% in table salt. In Europe, it is also approved as a food additive with the E-number E552. Actual concentrations in commercial table salt are typically much lower than the maximum permitted levels.
For example, one analysis of Morton's table salt indicates the presence of 0.2% to 0.7% calcium silicate. A 2007 study on production averages from Sifto Salt Corporation found the level to be 0.250%. These low concentrations are highly effective for preventing caking without altering the taste or nutritional profile of the salt.
Calcium silicate vs. other anti-caking agents
Table salt manufacturers can use several different anti-caking agents, and regulations vary by region. The following table compares calcium silicate with other common additives.
| Anti-Caking Agent | Common Use | Typical Amount in Salt | Regulatory Status |
|---|---|---|---|
| Calcium Silicate | Table Salt, powders | 0.2% - 0.7% | FDA GRAS, EU approved (E552) |
| Silicon Dioxide | Table Salt, powders | Up to 1.0% (in some regulations) | FDA GRAS, EU approved (E551) |
| Sodium Ferrocyanide | Salt (Europe, Kosher) | Very low, e.g., 13 ppm | Approved in some regions, highly regulated |
| Magnesium Carbonate | Table Salt, some specialty salts | Up to 1.0% | FDA GRAS |
Is it safe to consume?
Due to its GRAS status from the FDA and approval by other international bodies like the Joint FAO/WHO Expert Committee on Food Additives (JECFA), food-grade calcium silicate is considered safe for human consumption at the levels used in table salt. Its purpose is purely functional, with no evidence of long-term adverse health effects from typical dietary exposure. While the European Food Safety Authority (EFSA) noted a lack of long-term toxicity data in a 2018 report, they also reported very low absorption, indicating a low level of concern for safety at the quantities used.
It's important to distinguish between food-grade calcium silicate and industrial forms. Industrial-grade calcium silicate, such as that used for insulation, can have different properties and may pose health risks if inhaled, but this is not relevant for food products. Food-grade additives are produced under strict safety and purity standards.
Conclusion
In summary, calcium silicate is a widely used and carefully regulated anti-caking agent found in low concentrations in many brands of table salt. Its presence, typically between 0.2% and 0.7%, serves the practical purpose of keeping salt free-flowing by absorbing moisture. Global food safety authorities, including the FDA, have deemed it safe for consumption at these levels. For consumers concerned about food additives, options like specialty salts or kosher salts may use different anti-caking agents or none at all, but for the vast majority of people, the tiny amount of calcium silicate in their table salt poses no health risk.
