1. What Nixtamalization Is
Nixtamalization is the cooking and steeping of dried corn in an alkaline solution - traditionally calcium hydroxide, known as cal or slaked lime, and in some regions wood ash lye. The word comes from Nahuatl: nextli, ashes, and tamalli, dough.
Practically, the corn is simmered in water with the alkali, then left to steep for several hours or overnight. It is then drained and rinsed, with the loosened hulls rubbed off. What comes out is nixtamal, which is ground into masa.
The process does four separate things at once, and it is worth separating them because they are usually collapsed into a single vague claim about nutrition.
2. The Nutritional Effect: Freeing Bound Niacin
Corn contains niacin, vitamin B3, but most of it exists as niacytin - niacin bound into complexes with hemicellulose and small peptides. Human digestion cannot break these bonds meaningfully, so the niacin passes through unabsorbed. On paper the corn contains the vitamin. In the body it does not deliver it.
Alkaline treatment hydrolyses those bonds. The niacin is released into a form the gut can absorb. A diet heavily dependent on nixtamalized corn is therefore substantially better protected against niacin deficiency than one dependent on the same corn untreated.
There is a second, subtler nutritional effect. Corn protein is limited in the amino acid tryptophan, which the body can convert into niacin. Nixtamalization improves the availability of amino acids and shifts the amino acid balance somewhat, which contributes on the same axis.
And a third, often overlooked: the corn takes up calcium from the lime. Masa is a meaningful dietary calcium source, which matters in a food system without much dairy.
3. The Structural Effect: Why Masa Holds Together
The nutritional story gets told most often, but the physical story is why cooks kept doing it.
The alkali attacks the pericarp, the tough outer hull, degrading it so it can be rubbed away. It also partially breaks down the cell walls of the endosperm and begins to gelatinise the starch. The corn softens enough to grind into a cohesive dough.
Untreated dried corn ground into flour does not behave like masa. It produces a gritty meal that will not form a pliable dough or a tortilla that holds together when folded. The plasticity of masa - the thing that makes a tortilla a tortilla rather than a cracker - is a direct result of the alkaline cook restructuring starch and protein.
Flavour changes too, and distinctly. The characteristic aroma of a fresh tortilla is not the smell of corn; it is the smell of nixtamalized corn, and it is not reproducible any other way.
4. The Historical Lesson
Corn spread out of the Americas rapidly after the fifteenth century and became a staple across southern Europe, parts of Africa, and elsewhere. The grain travelled. The technique did not.
What followed, wherever populations became heavily dependent on untreated corn, was pellagra - the niacin-deficiency disease characterised by dermatitis, diarrhoea, dementia and, untreated, death. It appeared in northern Italy, in Spain, in Egypt, and later in the southern United States, where it persisted into the twentieth century and killed a large number of people.
For a long time it was blamed on a toxin in spoiled corn, or on an infectious agent. The eventual identification of it as a dietary deficiency - and specifically as a deficiency that Mesoamerican foodways had solved long before - is one of the more pointed episodes in the history of nutrition science.
The general lesson generalises well beyond corn: traditional processing methods frequently encode necessary chemistry that is invisible if you look only at the ingredient. Soaking legumes, fermenting cassava to remove cyanogenic compounds, leaching acorns - these are not quaint steps. They are the reason the food is edible.
5. Doing It, and What the Shortcuts Cost
The home process is straightforward but slow. Dried field corn - not sweet corn - is simmered with cal at roughly 1% of the corn's weight, then steeped for several hours or overnight, drained, and rinsed thoroughly with the hulls rubbed off. It is then ground, traditionally on a metate, now usually with a mill.
Two practical notes. Use food-grade calcium hydroxide specifically - it is sold for exactly this purpose and is not the same as construction lime. And rinse properly: under-rinsed nixtamal tastes soapy and alkaline.
What the products on the shelf actually are
Masa harina is nixtamalized corn that has been dried and milled into flour, then rehydrated by the cook. It is genuinely nixtamalized, so the nutritional and flavour changes have happened. Compared with fresh masa it loses aromatic complexity and some textural quality, but it is the real process in a shelf-stable form.
Cornmeal, polenta and grits are not nixtamalized. They are ground corn. They are excellent at what they do and there is no reason to treat them as deficient in the context of a varied diet - the pellagra story is about near-total dependence on untreated corn, not about eating polenta. But they will not make a tortilla, and no amount of technique will make them behave like masa.
Corn flour or cornstarch is a different product again and is not a substitute for masa harina in any application.
This is one of the clearest cases in cooking where a substitution genuinely cannot be made, and knowing why turns it from an arbitrary rule into an obvious one.
Frequently Asked Questions
What does nixtamalization actually do to corn?
Four things at once. It hydrolyses the bonds holding niacin in a bound form called niacytin, making the vitamin absorbable. It adds dietary calcium from the lime. It degrades the tough outer pericarp so the hulls can be removed. And it partially breaks down cell walls and gelatinises starch, which is what allows the ground corn to form a cohesive, pliable dough rather than a gritty meal.
Why did corn cause pellagra in Europe but not in Mesoamerica?
Because the grain travelled and the technique did not. Corn contains niacin bound as niacytin, which human digestion cannot release. Nixtamalization frees it. Populations in southern Europe, Egypt and the southern United States that became heavily dependent on untreated corn developed pellagra - niacin deficiency - while Mesoamerican foodways, which had used the alkaline cook for thousands of years, did not.
Is masa harina really nixtamalized?
Yes. Masa harina is corn that has been properly nixtamalized, then dried and milled to a flour that the cook rehydrates. The nutritional and flavour transformations have genuinely occurred. Compared with fresh masa it loses some aromatic complexity and textural quality, but it is the real process in shelf-stable form - not a shortcut around it.
Can I use cornmeal or polenta instead of masa harina?
No, and this is one of the few substitutions in cooking that genuinely cannot be made. Cornmeal, polenta and grits are simply ground corn - they have not been through the alkaline cook, so the starch and protein have not been restructured and the dough will not become pliable or hold together. They are excellent for what they do, but no technique will make them behave like masa.
What kind of lime do I use, and how much?
Food-grade calcium hydroxide, sold specifically for nixtamalization - it is not the same product as construction lime. A common ratio is roughly 1% of the weight of the dried corn. Rinse the cooked nixtamal thoroughly afterwards and rub the hulls off; under-rinsed nixtamal carries a distinctly soapy, alkaline taste.