How Does Popcorn Pop?

How Does Popcorn Pop?

Dec 26, 2023Mark Midwin

When you are enjoying some delicious popcorn, do you ever wonder how popcorn pops? How popcorn pops is an exciting mix of physics and chemistry! When a popcorn kernel is heated, the tiny amount of moisture in the kernel heats up, turns to steam, and pops the kernel into popcorn.  


The secret science behind how popcorn pops is in the hull of the popcorn kernel! If you were to take a microscopic look at a popcorn kernel, popcorn kernels have two layers, and these two little layers are very important for the popcorn to pop. The outside layer of the popcorn kernel is the layer most people might be familiar with. This special yellow layer known as the hull is the secret science to perfectly popped popcorn. If the hull of the popcorn is intact, it is impervious to moisture. Meaning the hull does not allow any of the moisture trapped in the popcorn kernel to escape until the hull is broken. This is where the fun science starts when wondering how popcorn pops.

The second layer of a popcorn kernel is called the endosperm. The endosperm is made up of hard starch and a tiny amount of moisture. For popcorn to pop there needs to be at least 14% moisture in the endosperm of a popcorn kernel. The endosperm starch is very hard before a popcorn kernel pops into puffy popcorn. You could save a trip to the dentist by not biting down too hard on un-popped popcorn kernels!



So, how does popcorn pop? The science behind how popcorn pops lies in the hull and the endosperm working together in unison to create a fun and flavorful science experiment. As you heat the popcorn kernels, the moisture in the endosperm is pushed past the boiling point at above 212 degrees Fahrenheit. As the moisture in the popcorn starts to boil, the moisture is converted into steam. The steam creates a lot of pressure on the hull of the popcorn kernel and gelatinizes the starch within the endosperm of the popcorn kernel. As the starch turns into a starchy jelly and the steam creates more and more pressure on the airtight hull, the strength of the steam and starch becomes too strong for the hull to contain, the hull of the popcorn kernel ruptures, and POP! The steam rushes out of the broken hull in a hurry and pushes the gelatinized starch out of the hull with it. Once the starch has puffed out of the hull, it quickly cools and becomes a puffy airy solid once again. This causes the popcorn to puff into the iconic fluffy popcorn we all know and love to eat. Alternatively, it is this same process which can cause popcorn kernels not to pop, if the hull is broken before the popcorn kernels are heated up, the steam can escape before pressure builds enough to pop the kernels into popcorn.

Who knew every time you popped popcorn you were conducting a fun and tasty science experiment. Popping popcorn is like watching a steam locomotive happen before your very eyes. So, how does popcorn pop? Steam pressurizes inside the hull and then pops into America’s favorite snack!

More articles