|Why does popcorn pop? - AB
Inside the hard, dry hull of a popcorn kernel is a portion of moist starch. When you heat the kernel well above the boiling temperature of water, the water in the starch converts to hot, high-pressure steam. The hotter this steam gets, the higher its pressure rises and the stronger the outward forces it exerts on the hull. Eventually, the hull rips open under the stress and exposes the starch to the low-pressure air around it. The pressurized steam then pushes the starch outward, expanding it to many times its original size. The kernel "pops."