Corn and Nixtamalisation.
When maize crossed the Atlantic without the Mesoamerican habit of cooking it with lime, it brought a disease no one in Mexico had: pellagra.
Maize kernels are hard, with a tough hull (pericarp), and their niacin (vitamin B3) is bound in a form the body cannot use, while their proteins are short of the amino acid tryptophan from which the body could make niacin. For at least three thousand years, Mesoamerican cooks have solved all of this at once: they simmer dried maize in water with cal — calcium hydroxide, slaked lime — then steep it overnight. The strongly alkaline water (V.7) loosens and partly dissolves the hull, which is rubbed off; releases the bound niacin; adds calcium; and changes the kernel's proteins and starch so that, ground wet, it forms masa, a dough that holds together and rolls into tortillas.
The treated kernels are nixtamal; whole, they are hominy (pozole); ground, masa; dried and powdered, masa harina. Nixtamalisation also gives tortillas their distinctive flavour and lowers some mould toxins. Where maize was adopted without it — southern Europe, the American South — people living mostly on maize developed pellagra: dermatitis, diarrhoea, dementia and death, until in the early twentieth century Joseph Goldberger showed it was a dietary disease. The workshop limes the water.
Below: the pH of the steeping water from the lime you choose, as a share of the maize's weight in twice its weight of water, at room temperature and near the boil (dissolved lime capped at its solubility; pH from the hydroxide in solution at 25 °C).
- Explain what nixtamalisation does.
- Explain the link to pellagra.
- Make masa from dried maize.
- Tell hominy, masa and masa harina apart.
Lime, simmer, steep, rinse, grind
With 1 % lime in twice the maize's weight of water, the dose (5 g/L) is more than water can dissolve, so the steep is saturated: pH about 12.3 near the boil and 12.7 as it cools overnight — strongly alkaline, like the lye of pretzels or 碱水 at its strongest. More lime does not raise the pH further; it stays as a sediment and is rinsed off. That is why recipes vary in how much lime they use without much changing the result, and why the kernels must be rinsed well before grinding.
Method: simmer 1 kg dried field maize with 10 g of cal (food-grade calcium hydroxide; it is caustic, so keep it off skin and out of eyes) in 2–3 litres of water for 20–40 minutes, until the hulls slip off when rubbed; leave to steep overnight; drain, rinse and rub off the loosened hulls; grind wet in a stone mill or strong food processor with a little water into masa. Press into tortillas and cook on a dry, hot comal about a minute a side until they puff. Masa harina, mixed with warm water, is the convenient route.
Make tortillas from masa harina and water: press, and cook on a hot dry pan until speckled and puffed. Taste a corner against a wheat tortilla.
Terms
- Nixtamalisation
- Cooking maize in alkaline lime water.
- Cal
- Food-grade calcium hydroxide, slaked lime.
- Masa
- Dough of ground nixtamal, for tortillas and tamales.
- Pellagra
- A disease of niacin deficiency, once common on maize diets.
Sources
- CRC Handbook of Chemistry and Physics: solubility of calcium hydroxide 1.73 g/L at 20 °C, falling to about 0.66 g/L at 100 °C; sodium carbonate pKa2 (bicarbonate) 10.33 at 25 °C.
- H. McGee, On Food and Cooking: The Science and Lore of the Kitchen, 2nd ed., Scribner, 2004.
- A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.