Here's an undeniable fact: when you make popcorn -- no matter what brand you use, no matter how closely you follow the directions -- some kernels just won't pop. Here's another undeniable fact: at some point someone labeled those unpoppable kernels "Old Maids." That person was not Bruce Hamaker, who has never used the phrase but has received hate mail from people saying he's sexist because of it. They've got the wrong guy. Bruce Hamaker's only connection to unpopped kernels is entirely inoffensive. He has figured out why they don't pop.

Popability depends on water. As the kernel heats up, water inside it releases steam, putting more and more pressure on the kernel until it explodes. In a recent study, Hamaker, a Purdue University food chemist, found that popcorn with lower water content left more unpopped kernels. "That," he says, "led us to the obvious question, What causes low moisture in certain kernels?" Which led straight to the hull, the crunchy outside of the corn.

The hull is made up of several thin sheets of cellulose. Turns out, when cellulose gets hot, it changes structure. Its thin sheets become crystals that bond so tightly together, water can't pass through. The more crystalline the hull becomes, the less water can leak out, and the more likely it is to pop. So the key to maximum popability is using popcorn strains whose hulls become most crystalline.

According to the Popcorn Board, a nonprofit organization of popcorn processors devoted to encouraging popcorn consumption, Americans consume a stunning 17 billion quarts of popped corn every year. So there's serious incentive to maximize popping potential. But Hamaker has no plans to transfer his findings into new and improved popcorn. "I'm a scientist," he says. "I'm more interested in big questions, like why some popcorn doesn't pop."