Popcorn pops because each kernel contains moisture inside a hard outer shell called the hull. When heated, the moisture turns into steam, building pressure inside the kernel until the hull bursts open. This sudden release of pressure causes the starch inside to expand and puff out as it cools, creating the fluffy popcorn. The popping sound is caused by the sudden release of steam pressure as the kernel explodes.
How Popcorn Pops
- Each kernel has moisture (~13.5-14%) trapped inside a hard starch surrounded by the hull.
- Heating converts the moisture to steam, raising internal pressure to around 135 psi.
- The pressure causes the hull to rupture explosively.
- The gelatinized starch inside inflates and solidifies into the familiar fluffy shape as it cools.
- Some kernels fail to pop if their hulls are cracked or moisture is too low.
The Popping Sound
- The "pop" sound comes from water vapor rapidly escaping and causing vibrations inside the kernel.
- This sound is separate from the hull rupture and the corn jumping in the air.
In summary, the primary cause of popcorn popping is the steam pressure buildup inside the kernel's strong hull, which bursts open and puff the starch inside.