Why Does Popcorn Pop?

Why does popcorn pop? Well, popcorn is a truly amazing food. Just think about that little kernel—only several millimeters in diameter—and how it explodes into a fluffy, tasty, white wonder that is 40-50 times bigger than the kernel itself.


Why Does Popcorn Pop? The Simple Explanation

Why does popcorn pop? Each un-popped kernel has inside of it a small amount of water. It is the water that is the secret to the kernel popping into popcorn.

There are three elements that are needed for popcorn to pop:

1.   Moisture inside the kernel

2.   Starch inside the kernel

3.   The hard shell surrounding the kernel

When the kernel is heated quickly, the water inside the kernel expands and turns to steam. The steam causes pressure to build up inside the kernel.

When the pressure inside the kernel is stronger than the strength of the kernel wall, the kernel pops. The soft tissues from inside the kernel puff out and you have popcorn. The fluffy white solid we eat is formed from the starch inside the kernel. Neat stuff. And that is the easy explanation as to why popcorn pops.


Why Does Popcorn Pop? The More Detailed Explanation

A popcorn kernel is made up of four parts:

·         the pericarp

·         the endosperm

·         the germ

·         the tip cap

The pericarp (also known as the bran or hull) is the outer shell. The endosperm is the starchy part that forms the bulk of the kernel with smaller amounts of protein, fat, minerals, and water. The germ is the embryo that sprouts and is not part of the popping process. The tip cap is where the kernel joins or attaches to the cob.

Popcorn pops because each kernel of popcorn contains a certain amount of moisture (13 to 14%), and oil. The outer hull of a popcorn kernel (pericarp) is strong and impervious to moisture. The starch inside the kernel consists almost entirely of a hard type.

As the oil and water within the kernel are heated past the boiling point, they turn the moisture in the kernel into a superheated pressurized steam which is contained within the moisture-proof hull. The starch inside the kernel gelatinizes, softens, and becomes pliable.

The pressure continues to increase until the breaking point of the hull is reached when the pressure is about 135 psi and the temperature is 356 degrees F (180 degrees C).

Then the hull ruptures rapidly which causes a sudden drop in pressure inside the kernel and a corresponding rapid expansion of the steam. This expands the starch and proteins of the endosperm into airy foam. As the foam cools rapidly, the starch and protein polymers set into the familiar crispy puff that we know as popcorn.


Why Don't All Kernels Pop?

In every batch of popcorn that is popped, there are always a few kernels that either crack open without popping, or do not pop at all. There are several possible reasons why these kernels don’t pop:

·         the hull may have been cracked and pressure didn't build up;

·         the hull may be too thick;

·         low moisture content within the kernel kept it from popping;

·         improper heating can keep the kernel from popping.


And that, my friends, answers the question, why does popcorn pop.

For a more scientific explanation of why popcorn pops, check out this link from Scientific American.