What is Cornstarch and How Does it Work?

Composition

As its name suggests, cornstarch is a starch that comes from the endosperm of a corn kernel. Endosperm is the tissue that surrounds the embryo in seeds of most flowering plants. In the case of corn, the endosperm makes up the majority of the part you eat. Cornstarch is not the same as corn meal, which is made by grinding up whole dried corn kernels.

Common Uses

In cooking, cornstarch is used as a thickening agent in soups, stews, and sauces. In baking, you will often see cornstarch in recipes for things such as pastry cream and other custards or in pie fillings.

Cornstarch can also be added to flour when baking to soften the texture of cakes (see this post about different types of flour for more details). Its absorbency also makes it a good anti-caking coating for things such as shredded cheese.

The Science of Thickening

Cornstarch contains long chains of starch molecules. The bonds of these molecules break down when exposed to moisture and heat above 203 °F (95 °C). When this happens, the starch molecules swell and take on more water causing a thickening effect. This process is called starch gelatinization and is irreversible.

When using cornstarch in cooking and baking, it should first be mixed with a small amount of room temperature liquid before it is added to the warm soup, stew, or sauce. This allows the starch molecules to spread out throughout the hot liquid more easily. Dumping cornstarch into a hot liquid all at once can lead to rapid gelatinization and clumping.