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Introduction
Calcium hydroxide (Ca(OH)₂), also known as slaked lime or hydrated lime, is a moderately strong base used in food processing for a variety of purposes, including pH adjustment, water treatment (lime softening), in the processing of corn (nixtamalization), in sugar refining, and as a firming agent. Unlike sodium or potassium hydroxide, calcium hydroxide has low solubility in water (about 1.7 g/L), so it is used as a suspension (limewater).
Calcium hydroxide is valued because it provides calcium ions in addition to alkalinity. In nixtamalization (processing corn for tortillas and hominy), the calcium ions chemically modify the corn to improve nutritional quality and flavor. It is also used in pickling to maintain crispness of vegetables.
CAS Number
1305-62-0
Synonyms
Slaked lime, Hydrated lime, Lime water (solution), Calcium hydrate, Pickling lime, E526 (EU).
Topic Headings
1. Nixtamalization: ancient technology for corn processing (paragraph form)
Nixtamalization is a process developed by Mesoamerican cultures thousands of years ago. Maize (corn) is cooked and soaked in an alkaline solution, traditionally limewater (calcium hydroxide suspension). The corn is boiled in 1-2% calcium hydroxide solution for 30-60 minutes, then allowed to steep for 8-16 hours. The alkaline treatment causes the pericarp (outer hull) to soften and loosen, which is then washed off. More importantly, it modifies the corn proteins and makes niacin (vitamin B3) bioavailable — without this treatment, diets based solely on corn cause pellagra (niacin deficiency). The calcium ions also cross-link pectin in the cell walls, giving the masa dough better cohesiveness for tortillas. Additionally, the process reduces mycotoxin levels (aflatoxins). The resulting hominy or masa is ground into dough for tortillas, tamales, and other Latin American dishes. Nixtamalization also improves the calcium content of corn products, as calcium from the lime is incorporated into the grain.
2. Physical and chemical properties (list form)
• Appearance — White powder or granules.
• Odor — Odorless.
• Molecular weight — 74.09 g/mol.
• Melting point — 580°C (loses water to form calcium oxide).
• Solubility in water — 1.73 g/L at 20°C (low solubility; forms a saturated solution called limewater with pH about 12.4).
• Solubility in other solvents — Insoluble in ethanol; soluble in glycerol and sugar solutions.
• pH (saturated solution) — 12.4 (strongly alkaline).
• Density — 2.21 g/cm³.
• Hygroscopicity — Slightly hygroscopic; absorbs CO₂ from air to form calcium carbonate.
• Heat of hydration — Exothermic when mixed with water (lime slaking).
3. Food applications and typical usage levels (list form)
• Nixtamalization of corn (tortillas, hominy, tamales) — 1-2% calcium hydroxide (by weight of corn); cooking and steeping.
• Pickling (cucumbers, peppers, etc.) — 0.1-0.5% in brine; firming agent (provides calcium ions).
• Sugar refining (cane and beet) — 0.1-0.5% to precipitate impurities and adjust pH; also used in carbonatation process.
• Water treatment (drinking water) — As lime softening to remove hardness and adjust pH.
• Fruit and vegetable preservation — Used in some traditional recipes to keep canned fruits firm.
• Candied fruit (e.g., citron) — Soaking in limewater to firm the fruit before sugar infusion.
• Alcoholic beverage production — For pH adjustment in some wine and cider processing.
• Egg preservation — Historically, eggs were preserved by coating with limewater (water glass method).
4. Regulatory status and safety (paragraph form)
Calcium hydroxide is approved as a food additive (E526) in the EU and as GRAS by the FDA under 21 CFR 184.1205 (as a processing aid). JECFA has not set an ADI because it is used as a processing aid and residues are low. For nixtamalized corn products, residual calcium hydroxide is neutralized by washing and cooking; the final product has pH near neutral. Maximum usage in EU: 2 g/kg in pickled vegetables (as firming agent) and 5 g/kg in sugar refining. Safety: calcium hydroxide is caustic and can cause skin, eye, and respiratory irritation in concentrated form. In food plants, dust control and protective equipment are needed. However, for consumers, properly prepared foods containing calcium hydroxide are safe. In fact, nixtamalized corn products provide significant dietary calcium. The only caution: ingestion of large amounts of dry calcium hydroxide (by accident) could cause severe gastrointestinal burns. In pickling, high concentrations of lime can make the product too alkaline and cause a soapy taste; correct dosing is critical.
