What makes cornstarch thicken liquids?

What do gravy, coffee cake, and icing on your birthday cake have in common? Well, they most likely were made using cornstarch.

As the name says, cornstarch is the starch of corn. It is usually extracted from the endosperm of the kernel of corn. If you have ever ran cornstarch through your fingers you know that it has very unique feel, almost like talcum powder. This texture actually acts as an anti-caking agent in confectioners sugar and cake flour. Actually, if you are ever in need of cake flour for a recipe but are clear out of it in the pantry, add 2TBSP cornstarch for every 1 cup all-purpose flour and voila...cake flour. (You will want to sift these ingredients together to make sure they are equally distributed).

Cornstarch is most widely known for its thickening properties when added to hot liquids. As the cornstarch is heated (must be boiling to get the maximum amount of thickness), the molecules begin to break apart and they run into the other starch molecules. These starch molecules interlock to form a fort of net that creates a barrier for the water molecules. It slows down the water molecules from moving in the liquid. This promotes the thickening of liquids like gravy, soups, and sauces. Below is an image that I found at cdavies.wordpress.com/2006/10/05/starch/. I think this is a good visual. You can see the the water is basically being trapped between the starch molecules.