A dense, powdery "flour" obtained from the endosperm portion of the corn kernel. Cornstarch is most commonly used as a thickening agent for puddings, sauces, soups, etc. Because it tends to form lumps, cornstarch is generally mixed with a small amount of cold liquid to form a thin paste before being stirred into a hot mixture. Mixing it with a granular solid like granulated sugar will also help it disperse into a liquid. Sauces thickened with cornstarch will be clear, rather than opaque, as with flour-based sauces. However, they will thin if cooked too long or stirred too vigorously. Cornstarch is also used in combination with flour in many European cake and cookie recipes; it produces a finer-textured, more compact product than flour alone. In British recipes, cornstarch is referred to as cornflour.
From The Food Lover's Companion, Fourth edition by Sharon Tyler Herbst and Ron Herbst. Copyright © 2007, 2001, 1995, 1990 by Barron's Educational Series, Inc.