Thursday, January 20, 2011

Nixtamalization - Making Posole/Hominy

Photo by Sergio Salvador
Last week at the Los Ranchos winter market, I got the chance to chat with the farmers from Corrales Chile Company, who were selling dried blue corn and corn meal. They also sold little packets of pickling lime and explained how to do the nixtamalization process at home to make your own posole and masa!

Nixtamalization (don't you just love that word?) is the process of cooking dried corn in highly alkaline water, which removes the skin or pericarp of the kernel, and softens the corn to make it easier for grinding.

The resulting product, called nixtamal, posole, or hominy, develops a uniquely delicious taste and aroma as well as a chewy texture. It can then be re-dried or frozen as posole, or ground while wet to make fresh masa for tamales or tortillas, then dried to make masa harina (check out this great flowchart). Here is a great video on making tortillas, starting with your own fresh masa.

Nixatmalization is probably one of the greatest achievements of Mesoamerican civilization, enabling the rise of the sophisticated Aztec and Mayan societies.
The process makes corn significantly more nutritious, by releasing bound niacin (also known as Vitamin B3, nicotinic acid or nicotinamide) and tryptophan, an essential amino acid which can be metabolized into niacin. Without nixtamalization, people who eat a heavily corn-based diet can develop painful nutritional deficiencies such as pellagra, which was rampant in the Southern U.S. until its cause was finally discovered in the early 1900's. Nixtamalization also significantly reduces mycotoxins from fungus or mold growing on the corn, which is common when corn is stored improperly. If calcium hydroxide is used as the alkaline agent, it also adds calcium to the corn. New Mexico State University discusses this in a great little paper comparing the nutritional qualities of blue corn vs. white or yellow corn. They also found that blue corn was naturally higher in zinc and iron!

Mexican posole is different from hominy because of the type of lime used, which produces a characteristically nutty flavor and aroma. In Mexico, nixtamalization typically uses calcium hydroxide (variously known as slaked lime, pickling lime, builders' lime or “cal”) which is made by mixing calcium oxide (quicklime) with water. Calcium oxide can be made by burning calcium carbonate, which comes from naturally occurring limestone or seashells. Other cultures use wood ash, lye (sodium hydroxide), washing soda (sodium carbonate), or baking soda (sodium bicarbonate), both of which occur naturally in some mineral deposits.

I did a fair amount of research on the correct process. I started with the instructions from this article, which are quite good, but it wasn't totally clear to me how long you really need to cook the corn depending on the type. Blue corn can be denser than white or yellow, so I thought it might take longer. In fact, there are different types of corn with significantly different properties - "Indian corn" and popcorn are types of flint corn, whereas most field corn grown on a large scale is dent corn. I also wondered whether the objective was for the alkali to permeate all the way through the kernel, or just to remove the pericarp. Directions from different sources give cooking times ranging from as little as 15 minutes to an hour, but I finally concluded that for posole it mostly just depends how long it takes to loosen the skins from your particular corn. For masa, you don't need to cook the corn as long, but you soak it overnight so that the liquid really does permeate through the entire kernel, gelatinizing the starches so that when you grind it the dough sticks together nicely.

So here's my recipe:
2 pounds dried corn (you can even use popcorn)
5 Tbs pickling lime
1 gallon water

Add corn and lime to water in a large stainless steel pot and bring to a boil. The water will gradually turn cloudy and yellow. Simmer for 15 minutes, then check whether the skins are coming off - just remove some kernels with a slotted spoon and put them in a bowl of fresh water. If you see little flaky skins floating in the water when you rub the kernels between your fingers, it's done. Otherwise, keep simmering and checking every 15 minutes or so. This shouldn't take more than an hour. The kernels may still be fairly hard inside, but this is fine. If you like, you can leave it in the limewater to soak for a few hours or overnight, and it will take less time to cook when you're ready to make your posole stew. If you're going for masa, you'll need to soak it overnight, then rinse it as described below, then you can grind it in a food processor.

Stir the pot to get the sediment off the bottom and pour off the limewater. Refill the pot with fresh water. Rub the kernels together with your hands to get the skins off. Drain and refill the pot and keep rubbing the kernels together. Do this a few more times until all the skins are rinsed away. Now you can freeze the posole or use it immediately to make posole stew. So that's it - boil, soak (optional), rinse and rub - not too bad, extra-delicious and nutritious!
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