Kathleen O'Brien, age 16, of Ottawa, Ontario, Canada, for her question

WHAT MAKES POPCORN BURST?

Popcorn is a type of corn. Its kernels, when heated, burst into tasty white food.

A popcorn plant is smaller than most varieties of field corn, but the ripe ear has the same food value.

Each popcorn kernel has a tough covering and contains much starch. And each kernel will pop when it contains about 13.5 percent moisture and is heated to about 400 degrees Fahrenheit. When heated, the moisture changes into steam. The hard covering keeps the steam from escaping, causing pressure to build up inside the kernel. The pressure finally bursts the kernel. Good popcorn kernels expand from 30 to 35 times their size when popped.

Most commercial popcorn in the United States is grown in Indiana, Iowa, Nebraska and Ohio.