What is inside each kernel of popcorn that makes it pop when heated?

Tucked inside each kernel of popcorn is a tiny droplet of water, trapped alongside a soft, starchy center. The kernel's hard outer hull, known as the pericarp, is incredibly strong and moisture-proof. When heated, this hull acts like a miniature pressure cooker. The internal water turns into powerful steam, building immense pressure that has nowhere to escape.

At around 355°F (180°C), the pressure becomes too great for the hull to contain, causing it to rupture violently. This sudden release of pressure makes the superheated starch inside expand and solidify almost instantly, turning the kernel inside-out and creating the fluffy, white puff we love to eat. This is also why only certain types of corn can become popcorn; they need a hull that is strong enough to build pressure but will still burst at the right moment.

Kernels that fail to pop, often called "old maids," usually have a damaged hull that allows steam to leak out, preventing pressure from building. They might also have an incorrect amount of internal moisture to begin with. The perfect pop requires that small, perfectly contained bit of water to create the magic.