In the popcorn machine, the corn kernels begin to pop with a resounding sound, transforming from hard-shelled kernels into fluffy popcorn. Why do the kernels make a popping sound when they pop? How do kernels transform into popcorn? It turns out that during the heating process, the kernels are subjected to pressure, which causes a series of changes. How is the popcorn we love so much produced?

Why do kernels make a popping sound when they pop?

Heating causes the hard-shelled kernels to crack, magically transforming into white, fluffy popcorn.

Popcorn is a unique cereal. While all dry kernels can pop when heated, the husks of most cereals make a muffled sound. However, the cellulose fibers in the husk of popcorn are exceptionally densely packed, making it very hard and thick, which is why it’s possible for the kernels to make a popping sound when they pop.

The popcorn plant looks almost identical to sweetcorn, the only difference being that sweetcorn ears stand upright, while popcorn ears droop. The kernels are primarily composed of starch and water. Popcorn is dried along with the stalk until the kernels are dry and easy to peel.

At this point, the kernels have a moisture content of about 14%. As the kernels heat, this moisture converts to steam, and the resulting internal pressure causes the husk to pop.

For this reason, popcorn kernels should be stored in an airtight container to maintain their moisture content. This allows for sufficient steam to build up internal pressure when heated. Overripe kernels are too dry to pop, resulting in burnt, bitter kernels on the bottom of the pan.

Popcorn is whole-grain corn and high in fiber. When popped in an air popper rather than in oil, it has a significantly lower calorie count. Weight for weight, popcorn contains more antioxidants than most fruits and vegetables and more iron than beef.

The Popping Process and Changes of Popcorn:

1. Raw Kernels

Unpopped kernels: The hard husk encloses the starchy kernel and moisture.

2. Water Vapor Accumulates into Pressure

As the kernel heats, the moisture in the kernel turns into vapor at 100°C (212°F), but the vapor cannot escape the thick, tight husk.

3. The Shell “Pops”

Pressure continues to build, and at 180°C (356°F), the pressure inside the kernel reaches nine times atmospheric pressure. The “pop” of the husk is the sound of gas escaping.

Continued Pressure, Then a Pop

The process of turning a kernel into popcorn involves raising the kernel’s internal temperature, causing the moisture to convert into vapor. The thick husk traps the vapor, preventing it from escaping. Consequently, as the kernel heats, the internal pressure increases. When the temperature reaches 180°C (356°F), the pressure inside the husk reaches nine times atmospheric pressure, causing the kernel to pop with a loud bang.

4. Popping

The heat has cooked the starch inside. When the husk pops, the expanding starch creates elastic force, causing the kernel to pop upward.

5. Starch Expansion

The force of the steam causes the cooked starch inside to expand outward.

(As the kernel bounces and rotates, the starch inside turns inside out, expanding and then rapidly cooling.)

6. Fluffy Popcorn

In milliseconds, the kernel cools inside, solidifying into a crisp, starchy white popcorn that is approximately 40 to 50 times the size of the original kernel.

(After the husk pops, the entire expansion process takes only one-fifteenth of a second.)