Three major types of corn are grown in the United States. Sweet corn, used mainly as food, is grown on around 650,000 acres. Popcorn, also used mainly for food, is grown on from 175,000 to 200,000 acres. The kernels contain a hard form of starch at the sides and a soft type in the center. This latter starch shrinks as the kernel ripens resulting in the terminal depression.
Dent varieties vary in kernel shape from long and narrow to wide and shallow.
It is the type mainly grown in this country. Flint corn has the hard starch layer entirely surrounding the outer part of the kernel. Consequently, on drying the kernel shrinks uniformly and does not develop a depressed area. This type is little grown commercially. The starch consists almost entirely of amylopectin, while in ordinary corn the starch is near 30 percent amylose and the remaining 70 percent is amylopectin.