Nixtamalization

Nixtamalization is the process of cooking and soaking dried corn in an alkaline solution, usually water with calcium hydroxide, known as cal, slaked lime or pickling lime. It is not the citrus fruit. The treated corn, called nixtamal, is ground into masa, the dough for tortillas, tamales and pupusas, or left whole as hominy for pozole. The method comes from Mesoamerica and is thousands of years old.

How to do it

1. Rinse 1 kg (about 2 pounds) of dried field corn.
2. In a large non-aluminum pot, stir 2 tablespoons (about 20 g) of food-grade calcium hydroxide into 3 liters (12 cups) of water.
3. Add the corn and bring to a boil, then simmer for 20 to 45 minutes, until the skins slip off when you rub a kernel.
4. Turn off the heat, cover and leave to soak for 8 to 24 hours.
5. Drain and rinse well, rubbing the kernels between your hands to remove the loose skins.
6. Grind the nixtamal while wet into masa.

Why it works

The alkaline water dissolves the tough outer skin of the kernel, the pericarp, so it can be rubbed off. It also changes the corn's starch and proteins, so the ground corn holds together into a dough. Plain ground corn will not. Most important, it frees niacin, a B vitamin bound up in corn that the body cannot otherwise use. It also adds calcium, and gives masa its typical flavor.

Substitutes

Dried masa flour, masa harina, is made from nixtamalized corn and only needs water. Cornmeal is not a substitute; it is plain ground corn and will not form a dough.

Common mistakes

• Using quicklime (calcium oxide) or lime meant for building. Use food-grade calcium hydroxide only, and keep it away from eyes and skin.
• Using an aluminum pot, which the alkaline water attacks.
• Not rinsing well, which leaves a bitter, soapy taste.
• Overcooking the corn, which gives sticky, gummy masa.

In recipes

"Nixtamal", "masa" and "hominy" all point to nixtamalized corn. Some home recipes use baking soda or wood ash as the alkali, which works in a similar way but tastes different.