Cookbook:Cornstarch

| Basic foodstuffs | Cereal | Corn

Cornstarch, sometimes confusingly called "cornflour", is a pure starch made from corn. It is not to be confused with cornmeal or corn flour proper.

Production
Cornstarch production begins with the soaking of corn kernels to soften them before grinding them to a wet slurry. It is then sieved to remove large fibrous particles, then centrifuging it to separate out the pure starch. Once separated, the starch is dried to a powder.

Characteristics
Like other pure starches, cornstarch is a fine white powder, with somewhat of a squeaky texture when rubbed. When mixed into liquid and heated, cornstarch adds a glossy appearance and thickens the liquid, setting it even more once cooled. Compared to wheat flour, cornstarch has twice the thickening power with a less-noticeable flavor, making it popular in cooking. However, cornstarch-thickened liquids will thin again if exposed to prolonged heat or stirred too vigorously,  and freezing will cause the mixture to break and weep. To avoid these issues, some professionals will use "waxy" cornstarch, which is both derived from a special variety of corn and modified to be more heat- and cold-stable.

Selection and storage
Cornstarch is quite shelf-stable. As long as it is kept segregated from moisture in an airtight container, it will keep on the order of months to years.

Use
Like other starches, cornstarch is primarily used for its shortening, thickening, and drying powers. For example, it may be added to baked goods to interfere with gluten formation and tenderize the final product, and it can also help retain water in cookies to make them chewy instead of crispy. Cornstarch can also be applied to wet items, drying them off so that batter will stick—this is commonly done for deep-fat frying. It thickens liquids into sauces, makes custards more heat-stable, and stabilizes a variety of fillings.

To use cornstarch for thickening liquids, as with sauces and custards, the best method is to suspend the starch in a cool liquid before mixing it with a warm-to-hot liquid —this prevents undesirable clumping. The mixture is then gently heated up to a brief simmer to activate the thickening process, followed by removal from the heat to prevent subsequent breakdown and thinning.

Note that mixtures thickened with cornstarch will gradually break down and thin over the course of several days, and they should not be vigorously stirred, reheated, or frozen.

Substitution
When a recipe uses cornstarch to thicken liquid or absorb moisture, another starch or a gelling agent such as xanthan gum, pectin, agar, or gelatine can be an effective substitute (though not one-to-one). When a recipe uses cornstarch to make a crisp coating, you can often substitute cornmeal, some variety of flour, or another starch.