Cornmeal

Everything about industrial cornmaking follows from the structure of the kernel. The germ is large, oily, and tough; the bran is fibrous; the endosperm is brittle. Tempering toughens the germ and bran further so that a degerminator can shear them off in one piece rather than shattering them into the meal. The cleaner that separation is, the lower the oil and fibre in the resulting meal — and oil is what makes cornmeal go rancid.

Degerminated meal

Meal from which germ and bran have been separated. Lower in oil and fibre, and much longer-keeping.

Whole-grain cornmeal

Meal in which the whole kernel is ground with nothing removed, including stone-ground meal. Fuller flavour, shorter keeping.

Grits

The coarsest endosperm fraction, sifted out above meal size. Same material, larger particles.

This means "cornmeal" names two rather different products. Degerminated meal is a stable commodity that ships and stores; whole-grain and stone-ground meal keeps the germ oil and has a limited life. A specification that does not say which is being sold has not described the goods.

Cornmeal is eaten as thick and thin porridges across eastern and southern Africa, as polenta in northern Italy, as grits in the American South, and as the base of cornbreads and coatings worldwide. Colour follows the grain — yellow and white maize give yellow and white meal, and the preference between them is regional and strong.

Masa is not cornmeal. Tortillas and related foods are made from nixtamalised maize: the grain is cooked and steeped in an alkaline solution, which loosens the pericarp, changes the starch and protein, and releases bound niacin. That is a chemical process with a different product, not a fineness of grind, and grinding dry cornmeal will not produce it.

Cornmeal is specified by particle size distribution, by the residual fat that indicates how completely the germ was removed, and by ash and fibre, which indicate residual bran. Colour and freedom from dark specks matter to buyers. Moisture governs keeping quality, as with any milled product.

Two risks dominate storage. Rancidity is a function of how much germ oil is left, so degerminated meal outlasts whole-grain meal by a wide margin under the same conditions. And mycotoxins pass through milling: aflatoxins and fumonisins present in the grain are not destroyed by grinding, and they distribute unevenly between the fractions. Meal made from contaminated maize is contaminated meal, and the regulatory limits apply to it in its own right.