Popcorn pops when trapped water inside the kernel turns to steam and bursts the hull.

The longer version

Each popcorn kernel holds a small amount of water sealed inside a hard, mostly airtight hull surrounding a dense starchy interior. Heating turns that water into steam, and pressure builds until the hull can no longer contain it, roughly around the point where the starch has softened into a gel.

The kernel ruptures, the pressure drops instantly, and the expanded starch sets into the foam-like shape people eat. Kernels that fail to pop usually leaked moisture through a cracked hull during storage. The variety matters too, since only certain types of maize have hulls strong enough to hold pressure, which is why ordinary field corn does not behave the same way.

Where this entry sits

Everyday ingredients turn out to be full of quiet chemistry and long history. This collection gathers short, plain explanations of how bread rises, why onions sting, where common spices originate, and how coffee, tea, and chocolate reached the modern kitchen. The full list sits on the Food and Drink page, where every entry is listed in order.