High-Speed Video: Popcorn Popping @ 6,200 FPS | Modernist Cuisine: The Art and Science of Cooking

The key to why pop­corn pops is its unusual moisture-proof hull. As the ker­nel is heated beyond the boil­ing point, the water inside begins to turn into steam and expand. Since the hull will not let steam out, the pres­sure inside the ker­nel begins to rise. The hull can han­dle a pres­sure of around 135 psi before burst­ing open. At this point, the pres­sure inside the ker­nel is released very rapidly, expand­ing the starch and pro­teins into a dense foam that sets quickly.