It's hard to believe that an exploding vegetable is one of the favorite snacks in the United States. But it is, and Americans swallow about 17 billion quarts of supersize corn kernels each year. Thousands of years before popcorn appeared in multiplexes, people in North and Central America were both eating it and wearing it, as puffy necklaces. Food chemists say the first wild corn was popcorn, which probably initially revealed its inflated goodness when tossed into a fire. Corn poppers, made out of fired clay, came next. Why does heat make popcorn pop? An American Indian folk tale explained it this way: Each kernel was home to a spirit, and as the popcorn was roasted, the spirits got madder and madder. They would shake their houses, and finally burst out in puffs of angry steam. Of the five basic kinds of corn, only one pops. Popcorn has an especially hard hull, or shell ("pericarp"). This shell allows a great deal of pressure to build up inside before it breaks. It's also perfect for keeping moisture in the kernel. About 14 percent of a popcorn kernel is water trapped in the endosperm - the starch inside. Unlike ordinary corn, popcorn contains more of a kind of translucent starch that expands smoothly. When the kernel is heated to 212 degrees, some of the water in the kernel turns to steam. The hard hull acts like the lid on a pressure cooker, forcing the steam into the grains of starch. This changes the starch into superhot, gel-like globs. The pressure-cooker effect allows the temperature in the kernel to soar well above the boiling point, to about 347 degrees. According to chemists, the pressure inside the kernel is about nine times that of Earth's atmosphere when the hull finally explodes, forced outward by steam and superheated water. Freed to expand in the lower-pressure room air, the steam and hot water carry the inner white starch outside, turning the kernel inside out and swelling it to 40 to 50 times its original size. The peculiar shape of the popped kernel, scientists say, comes from the starch granules, which expand like bubbles when the hull bursts open. As we all know, not every kernel pops. Why? A cracked hull makes for an unpopped kernel, because steam escapes before it can build up enough pressure. And the water content must be near 13.5 percent - just right - for popcorn to explode. Too dry, and there won't be enough steam to break through the hull. Too soggy, and the corn will pop into a small, heavy dud. Scientists who study popcorn have recently discovered what makes some popcorn kernels pop better than others. The poppiest kernels, they say, have an extremely tough hull, with a very orderly arrangement of cellulose molecules. The strong crystalline structure that forms when the kernel is heated holds moisture in better, so that each kernel explodes with full force.

---

Enjoy the Corn!