Food grade lime is a purified form of calcium hydroxide, a white powder used in cooking and food processing to firm textures, process corn, and adjust acidity. It has nothing to do with the green citrus fruit. You may also see it called slaked lime, hydrated lime, pickling lime, or by its Spanish name, cal. Its chemical formula is Ca(OH)₂.
The “food grade” distinction matters because calcium hydroxide is also sold for industrial and construction purposes. Food grade versions meet purity standards set by the FDA, which classifies calcium hydroxide as Generally Recognized as Safe (GRAS) with no specific concentration limit beyond standard good manufacturing practices.
How It Differs From Other Types of Lime
Calcium hydroxide starts as limestone, which is heated to produce quicklime (calcium oxide). When water is added to quicklime, the result is slaked lime, or calcium hydroxide. Industrial-grade and food-grade versions are chemically identical, but food grade lime is processed to remove heavy metals, silica, and other contaminants that would be harmful to eat. If you’re buying lime for any kitchen use, always confirm the label says “food grade.”
Nixtamalization: The Corn Connection
The most widespread culinary use of food grade lime is nixtamalization, the ancient Mesoamerican process of soaking dried corn in an alkaline solution. Corn kernels are cooked and steeped in water mixed with cal, then washed to remove the outer hull. The result is nixtamal, which gets ground into masa, the dough behind tortillas, tamales, pupusas, and hominy.
This isn’t just a texture trick. The alkaline soak transforms the corn nutritionally. Untreated corn locks away most of its niacin (vitamin B3) in a form your body can’t absorb. Lime breaks those chemical bonds and makes the niacin available. This is why populations that historically ate corn without nixtamalization, like parts of colonial-era Europe, developed pellagra, a niacin deficiency disease. The process also dramatically increases the calcium content of the corn itself. Research on nixtamalized corn found that calcium absorption increased roughly fivefold compared to untreated grain when using a standard concentration of calcium hydroxide.
Pickling and Firming Fruits
If you’ve ever had an exceptionally crunchy homemade pickle, food grade lime may be the reason. Soaking cucumbers or other vegetables in a lime-water solution before pickling makes them noticeably crisper. The calcium ions penetrate the vegetable’s cell walls and bind with natural pectin, reinforcing the structure so it holds up during fermentation or canning instead of turning soft.
The same chemistry works for fruit. Jams and jellies made with a calcium source produce a firmer set because the calcium strengthens the bonds within pectin. In Japanese cuisine, fermented plums (umeboshi) treated with calcium hydroxide have skins that resist tearing and a texture that sensory panels rated as significantly firmer than untreated plums. If you’ve ever wondered why some commercial canned fruits hold their shape so well, calcium hydroxide is often part of the answer.
One important note for home pickling: after soaking vegetables in lime water, you need to rinse them thoroughly (at least two or three times in fresh water) before adding your vinegar brine. The alkalinity of the lime can neutralize the acid that makes pickles safe for long-term storage if it isn’t fully washed away.
Other Culinary Uses Around the World
Food grade lime shows up in kitchens across cultures. In parts of South and Southeast Asia, it’s used to soak betel leaves and areca nuts. Chinese century eggs get their distinctive gel-like texture from a curing paste that includes calcium hydroxide. In some Latin American countries, lime water is used to soak fruit like figs or papaya before candying, keeping them intact through long sugar cooking. Sugar refining itself relies on calcium hydroxide to clarify raw cane juice, removing impurities before crystallization.
Safety and Handling at Home
Calcium hydroxide is strongly alkaline. A saturated solution has a pH of about 12.4, which puts it in the same range as household ammonia. In its dry powder form, it can irritate your skin, eyes, and lungs. Swallowing undiluted calcium hydroxide can burn the mouth, throat, and digestive tract, causing nausea, vomiting, and diarrhea.
For home use, the practical risks are modest as long as you treat it with basic respect. Wear gloves when mixing lime water, avoid breathing in the dust when opening the container, and keep it away from your eyes. If any dry powder or concentrated paste contacts your skin, wash it off with plenty of water. Store it in a sealed container away from children.
In the concentrations typically used for cooking (a tablespoon or two dissolved in a gallon of water, then food rinsed afterward), calcium hydroxide is safe. The amount that ends up in your final dish is small, and the FDA places no upper limit on its use in food beyond standard manufacturing practices. The key is never eating it straight or in concentrated form.
Where to Buy It
Food grade calcium hydroxide is sold at Mexican and Latin American grocery stores, often labeled “cal” or “cal para nixtamal.” You can also find it online or at specialty canning supply retailers under the name “pickling lime.” Expect to pay a few dollars for a bag that will last through many batches. Always check for a food grade label. Hardware store lime is chemically similar but may contain impurities that aren’t safe to eat.