What is E552?

Complete guide to understanding E552 (Calcium Silicate) in your food

The Quick Answer

E552 is calcium silicate, a white crystalline powder created synthetically from calcium and silicon compounds.

It’s used in food primarily as an anti-caking agent, preventing powders and granulated foods from clumping and maintaining free flow.

E552 is one of the most widely used anti-caking agents globally, particularly in table salt, dietary supplements, spices, baking powders, and cheese products. Its unique high water absorption capacity (2.5 times its weight) makes it exceptionally effective at trapping moisture before it can cause caking.

What Exactly Is It?

E552 is calcium silicate (Ca₂SiO₄), a synthetic inorganic compound created by combining calcium and silicon.

Unlike naturally occurring minerals, calcium silicate is manufactured through chemical synthesis. The result is a white crystalline powder with a unique loose, porous structure that gives it exceptional water-trapping abilities.

Calcium silicate is fundamentally different from pure calcium—the silicon component doesn’t come from sand or quartz in the final form but is chemically bonded with calcium to create a specific compound with anti-caking properties.

Chemical composition:

• Primary form: Ca₂SiO₄ (calcium orthosilicate)
• Hydrated form: xCaO·ySiO₂·zH₂O (with varying water content)
• CAS Number: 1344-95-2
• EC Number: 215-710-8
• Molecular weight: 172.24 g/mol
• Melting point: 2,130°C (indicating high thermal stability)

How it’s made:

Calcium silicate is synthesized through a three-step process:

• Step 1: Burnt lime (calcium oxide) or limestone is treated with hydrochloric acid to produce calcium chloride solution
• Step 2: The calcium chloride solution is mixed with clear sodium silicate (also called waterglass)
• Step 3: Calcium silicate precipitates out, is filtered, collected, and dried into the final white powder

Alternative production method: Calcium silicate can also be produced by reacting calcium hydroxide directly with sodium silicate, skipping the acid treatment step.

Important distinction: The 2018 EFSA re-evaluation emphasized that calcium silicate (E552) is NOT simply a mixture of silicon dioxide (E551) and calcium oxide. It’s a true chemical compound with distinct properties from either component alone.

Where You’ll Find It

E552 is used in a wide range of dry food products:

• Table salt and salt substitutes (most common use)
• Baking powder and leavening agents
• Dietary supplements and vitamin tablets
• Powdered sugar and icing sugar
• Spices and seasoning blends (preventing clumping)
• Powdered whey and powdered milk products
• Cheese products (sliced cheese, processed cheese)
• Dried soup powders and packet soups
• Bouillon cubes
• Powdered flavorings and seasonings
• Powdered herbs
• Food supplements in solid/powder form
• Chewing gum
• Dry cereals (in some formulations)
• Emulsifiers and colors (as carrier)
• Powdered confectionery
• Dried powdered foods

Regulatory use levels:

• FDA: Not to exceed 2% in table salt, 5% in baking powder
• EFSA: Classified as “additives other than colours and sweeteners” with specified uses in defined food categories

E552 is one of the most widely used anti-caking agents globally, though it often appears on labels simply as “anti-caking agent” or “E552” without prominence.

Why Do Food Companies Use It?

E552’s primary function is exceptional water absorption and moisture management in dry products.

Food manufacturers use calcium silicate for multiple strategic advantages:

• Water absorption: Absorbs water at 2.5 times its own weight—exceptional capacity
• Anti-caking: Traps moisture internally, preventing it from reaching product and causing caking
• Moisture barrier: Creates coating on product particles that repels external moisture
• Extended shelf life: Prevents degradation from moisture absorption during storage and transportation
• Van Der Waals reduction: Reduces molecular attraction between particles, improving flowability
• Free flow maintenance: Keeps powders, granules, and crystals loose and free-flowing
• Non-sticking: Prevents particles from adhering to each other or processing equipment
• Low addition levels: Effective at very low concentrations (typically <1%)
• Cost efficiency: Inexpensive per unit effectiveness
• Anti-foaming: Reduces foam formation during food processing
• Carrier function: Can serve as carrier for other additives, dyes, and emulsifiers
• Chemically stable: Doesn’t react with food ingredients or affect flavor/color
• Temperature stability: Remains stable at processing temperatures
• Inert: Doesn’t affect nutritional value or taste of products

Unique advantage in table salt: Salt crystals are hygroscopic—they naturally absorb moisture from air and reform crystals, causing caking. Calcium silicate’s exceptional water absorption prevents this by trapping moisture before it can recrystallize, making it nearly essential in salt manufacturing.

Is It Safe?

E552 is approved by major regulatory authorities and is considered safe for food use.

Regulatory approval:

• FDA approved: Generally Recognized As Safe (GRAS) for use in table salt (max 2%) and baking powder (max 5%)
• EFSA approved: Listed in Commission Regulation (EU) No 231/2012 as authorized food additive
• JECFA approved: ADI “not specified” (set in 1985) with function class as anti-caking agent
• Food Standards Australia New Zealand: Approved with code number 552
• International approval: Approved by UN FAO and WHO as safe in a large variety of products

Safety profile:

• ADI: “Not specified” by JECFA—indicating no safety concerns
• GI absorption: Very low absorption in gastrointestinal tract
• No genotoxicity: No evidence of genetic damage
• No developmental toxicity: No evidence of birth defects
• Low bioavailability: Calcium and silicon from E552 are not significantly absorbed
• Inert in body: Largely passes through digestive system unchanged
• No carcinogenicity: No evidence of cancer-causing potential
• No acute toxicity: No documented toxicity at food use levels
• Centuries of use: Silicon dioxide and silicates occur abundantly in nature and are part of normal human diet

2018 EFSA Re-evaluation findings:

The most recent comprehensive safety assessment (2018) found:

• Calcium silicate dissociates to limited extent in GI tract into silicates and calcium ions
• The resulting amounts of calcium and magnesium ions are not enough to disturb normal physiological processes
• No indication of genotoxicity or developmental toxicity
• Silicon accumulation in kidney and liver observed in rat studies (but at very high doses)
• Overall safety confirmed at approved use levels
• Note: “Safety cannot be fully assessed due to lack of reliable data on subchronic and chronic toxicity, carcinogenicity, and reproductive toxicity” (standard caveat noting that older additives don’t have complete modern toxicity batteries)

Natural vs Synthetic Version

E552 is entirely synthetic—it does not occur naturally in this exact form:

Source and production:

• Raw materials: Calcium compounds (limestone, chalk) and silicon compounds (sand, diatomaceous earth) are natural
• Processing method: Synthetic chemical precipitation (not natural fermentation or extraction)
• Final product: Not found naturally; manufactured in controlled conditions
• Regulatory classification: Synthetic additive, not a natural substance

Relationship to natural silicates: While silicon dioxide and natural silicates are abundant in nature and part of the normal diet, calcium silicate as a specific compound is synthetically manufactured. However, the chemical components (calcium and silicon) are natural minerals that occur in all foods.

Vegetarian/vegan/dietary status:

• Vegan: Yes—no animal products used in synthesis
• Vegetarian: Yes
• Kosher: Yes (pareve)
• Halal: Yes
• Gluten-free: Yes
• Dairy-free: Yes (despite containing calcium, it’s derived from limestone, not dairy)

Natural Alternatives

Want to avoid E552 or looking for alternative anti-caking agents?

Some alternatives include:

• E551 (Silicon dioxide) – Mineral anti-caking agent; made from quartz sand
• E553a (Magnesium silicate) – Synthetic magnesium silicate; similar function
• E553b (Talc) – Natural mineral talc; similar function
• E559 (Kaolin) – Natural clay; anti-caking properties
• E554, E555, E556 (Aluminium silicates) – Silicate-based alternatives with aluminum
• Modified food starch – Plant-based anti-caking agent
• Rice starch or cellulose – Natural plant alternatives
• Gum arabic or acacia gum – Natural alternatives
• Accept moisture absorption: Store products in dry conditions; accept occasional clumping

Comparison to Related Silicate Additives

E552 differs from other silicate anti-caking agents:

• E551 (Silicon dioxide): Pure silica from quartz sand; different mineral compound
• E553a (Magnesium silicate): Magnesium-based silicate; different properties
• E553b (Talc): Natural mineral talc; different structure and properties
• E554, E555, E556: Aluminium silicates; different element composition
• E559 (Kaolin): Natural clay; different mineral structure
• Key distinction: E552 has unique calcium component, making it suitable for calcium supplementation in some applications

The Bottom Line

E552 (calcium silicate) is a synthetically manufactured anti-caking agent with exceptional water absorption properties.

It’s found in table salt (most common use), baking powder, dietary supplements, spices, powdered sugar, and dried food powders—where it prevents caking and maintains free flow at very low concentrations.

E552 is approved by the FDA, EFSA, JECFA, and virtually all regulatory bodies worldwide with ADI “not specified,” indicating no safety concerns.

Key advantages: E552 absorbs water at 2.5 times its own weight—making it exceptionally effective. Its low bioavailability, inert nature, and decades of safe use provide strong safety reassurance despite some data gaps in comprehensive toxicity batteries.

For consumers: E552 is a well-established, extensively approved additive that serves a critical function in preventing food deterioration from moisture. Its primary dietary consideration is simply that it’s synthetic (not natural), but this doesn’t indicate any safety concern—it indicates it was intentionally designed for specific functional properties.

Primary application: E552 is nearly irreplaceable in table salt and similar granulated products where moisture management is critical for maintaining quality and shelf life. Its exceptional water absorption capacity makes it uniquely effective for this application compared to alternatives.