1. Critical temperature
Temperature is key; only 30 per cent of kernels pop when heated to 170°C, compared to over 90 per cent at the optimum 180°C.
2. Water content
Popcorn kernels are about 10-20 per cent water. When heated, the pressure in the kernel increases as the water vaporises.
3. Breaking point
Once the pressure inside the kernel reaches a certain level, the tough outer shell bursts open.
High-pressure steam escaping through the kernel fracture causes the characteristic popping sound.
As the kernels cook, starch molecules expand and soften to form spongy ‘flakes’.
Scientists discovered that a ‘leg’ of starch expanding against the pan’s surface propels the popping corn into the air.
The kernel appears to turn inside out as it rotates, with the soft, starchy innards expanding outwards.