From CNN:
The nuisance kernels have kept many a dentist busy, but their days could be numbered: Scientists say they now know why some popcorn kernels resist popping into puffy white globes.
It’s long been known that popcorn kernels must have a precise moisture level in their starchy center — about 15 percent — to explode. But Purdue University researchers found the key to a kernel’s explosive success lies in the composition of its hull.
More here.