What is E529?

Complete guide to understanding calcium oxide in your food

The Quick Answer

E529 is calcium oxide, commonly known as quicklime or lime.

It’s used in food production to regulate acidity, treat flour, and add calcium.

Most people never directly consume it, as it’s typically used as a processing agent rather than a food ingredient.

What Exactly Is E529?

E529 is calcium oxide (CaO), a white powder created by heating limestone to extremely high temperatures.

The process is ancient and simple: limestone (calcium carbonate, CaCO₃) is heated above 825°C (1,517°F). This releases carbon dioxide and leaves pure calcium oxide. This chemical reaction has been known since prehistoric times.

Calcium oxide is also called “quicklime” or simply “lime.” The name “quicklime” comes from the Latin word “vivus” (living) because when you add water to it, it releases tremendous heat and appears to “come alive.”

In technical terms, it’s a strongly alkaline compound—the opposite of acidic. But what matters for food consumers is that it’s an approved processing aid.

Where You’ll Find E529

E529 appears mainly in food manufacturing processes rather than as a visible ingredient:

– Sugar refining (clarifying sugar juice)
– Jam and jelly production
– Bakery products (as leavener and stabilizer)
– Drinking water treatment (indirect food use)
– Dietary supplements (as calcium source)
– Cocoa products
– Grain products

Unlike table salt or spices, you won’t see “calcium oxide” listed on most food labels because it’s primarily used as a processing aid—a temporary agent during manufacturing that becomes part of the finished product’s chemical composition rather than remaining as a distinct ingredient.

Why Do Food Companies Use E529?

E529 serves three main functions in food production.

First, it’s a powerful pH regulator. Because calcium oxide is strongly alkaline, it neutralizes acids in food production—critical in sugar refining where impurities need to be removed, and in bakery products where pH affects how bread rises and tastes.

Second, it acts as a flour treatment agent, improving the properties of flour for baking. This affects dough texture and baking performance.

Third, it serves as a source of bioavailable calcium for food fortification. Unlike many calcium compounds, calcium oxide provides calcium in a form your body can absorb.

So food companies use it because it solves real manufacturing problems while adding nutritional value.

Is It Safe?

Regulatory authorities say E529 is safe for use in food.

The FDA, EFSA, and WHO’s JECFA all approve it. No Acceptable Daily Intake (ADI) was established—which is actually a positive sign. When a substance’s ADI is “not determined,” it typically means there’s no concern about its use at approved food levels.

Calcium oxide is used under “Quantum Satis” authorization, meaning manufacturers use only the amount necessary to achieve the desired effect, with no absolute upper limit specified. This flexibility reflects confidence in its safety.

When tested in animal studies, calcium oxide showed no signs of acute toxicity, genotoxicity (genetic damage), carcinogenicity (cancer), or reproductive effects—even at very high doses.

Industrial Hazards vs. Food Safety

It’s critical to understand the difference.

Calcium oxide has serious occupational hazards that workers in cement plants, steelmaking, and chemical manufacturing must manage carefully. It can cause:

– Severe skin and eye irritation or burns from direct contact
– Respiratory irritation from inhalation of dust or aerosols
– In extreme chronic exposure: nasal passages, brittle bones

However, these hazards apply to workers handling pure calcium oxide powder in industrial settings—not to consumers eating food containing trace amounts of E529.

During food manufacturing, E529 is used in small quantities and typically converts to calcium hydroxide or other compounds during processing. By the time food reaches your table, any E529 has been either converted to other forms or exists in negligible quantities.

This is the same distinction as with salt: sodium chloride can be toxic in large quantities, but the trace amount in a serving of food is essential for health.

The Chemistry: Water Reaction

One unique property makes E529 interesting: its reaction with water.

When calcium oxide contacts water, it undergoes an extremely exothermic (heat-releasing) reaction. One liter of water combined with 3.1 kg of calcium oxide releases 3.54 megajoules of energy.

This intense heat release is used intentionally in self-heating food products and emergency cooking kits—allowing food to be heated without open flames or electricity.

From a consumer safety perspective, this reaction is safely contained in manufacturing and finished products. You won’t experience any heat effects from eating foods containing trace E529.

Natural Occurrence

E529 isn’t a synthetic laboratory invention.

Calcium oxide occurs naturally from limestone (a rock formed from ancient sea shells and coral). The process used to make food-grade E529 is simply controlled heating of this natural mineral—similar to how salt is mined and refined.

In fact, calcium oxide is one of the oldest substances humans have used. Archaeological evidence suggests it was used in prehistoric times, and it’s been essential to construction (mortar, plaster, concrete) for thousands of years.

Calcium Content and Nutrition

E529 can fortify foods with bioavailable calcium.

Calcium is essential for bone health, dental health, and muscle function. When used in dietary supplements or fortified foods, E529 provides calcium in a form your body can absorb and utilize—making it nutritionally valuable, not just a processing aid.

This dual function—serving both as a processing tool and a nutritional additive—is one reason regulatory agencies have approved it widely.

When Is E529 Actually Used vs. Calcium Hydroxide?

Calcium oxide and calcium hydroxide (slaked lime) are related but different.

Calcium hydroxide is calcium oxide after it’s been combined with water—the “hydrated” form. In food processing:

– Calcium oxide (E529) is used when pure, dry conditions are needed
– Calcium hydroxide (E526) is used when a water-based or slaked form is preferable

During manufacturing, E529 often converts to calcium hydroxide through hydration, so the final product may contain mostly the hydrated form despite starting with calcium oxide.

Historical and Industrial Uses

Beyond food, calcium oxide is fundamental to modern civilization:

– Steelmaking: Neutralizes acidic compounds, produces about 30-50 kg per ton of steel
– Cement production: Primary ingredient in Portland cement for construction
– Paper manufacturing: Used in kraft pulp processing
– Water treatment: Alkalinity and pH adjustment

This extensive industrial history and long-term safety record in human use supports its approval for food applications.

Vegan, Vegetarian, and Dietary Status

E529 is suitable for:

– Vegan diets ✓
– Vegetarian diets ✓
– Gluten-free diets ✓
– All religious dietary restrictions ✓

Calcium oxide is mineral-derived, with no animal products involved in its production or use.

The Bottom Line

E529 (calcium oxide) is an ancient, naturally derived chemical used as a food processing aid and acidity regulator.

Regulatory authorities worldwide classify it as safe for approved food uses.

While concentrated calcium oxide has serious occupational hazards, these don’t apply to consumers eating foods containing trace amounts of E529.

Unlike many food additives, E529 can actually contribute to nutrition by serving as a source of bioavailable calcium.

No Acceptable Daily Intake was set, indicating no concern about its approved uses.

As always, food labels must declare E529 when used, enabling informed consumer choice—though it’s often used as a processing aid not requiring label declaration.