Why Does Popcorn Pop?

Andy Waters
Latest posts by Andy Waters (see all)

Popcorn has such a long history that dates back thousands of years, however, it didn’t become popular or accessible until 1890. And since we first discovered the wondrous popcorn kernels that we know all so well today, we’ve been entranced by how they work!

When heated, they explode, that’s a generalized understanding and observation of the kernels that everyone can relate to. But, what exactly does happen when they pop in the microwave or in a steel pan?

That’s what we’re going to answer for you today so sit back and relax as we unpick every aspect of why popcorn pops so you don’t have to! You want an answer and we’re going to give you one! It’s a fascinating combination of chemistry and physics.

So, if you’ve fascinated by popcorn and want to get stuck into the in-depth science behind the structure of the kernels and how they pop because of pressure and physics, then find out below!

The Kernels Themselves

The kernels that we use to get to our well-known and delightful popcorn snack have two layers to them. The outer layer is a transparent hull with a yellowish hue to it, and this hull is the secret to getting your hands on the perfectly popped buttery goodness.

The hull itself is resistant to moisture so no moisture can be released until it is fully breached. This process acts as a pressure vessel during the popping duration. We told you this would be a bit of a science lesson!

Inside this hull is something called the endosperm, funny name right? This contains hard starch and a very small amount of moisture, like a minuscule amount of up to 14 percent. It’s absolutely rock hard before the popping process occurs which is why it hurts so much to bite into one on accident. And we’ve all been there…

Popping Failures

You know it first hand, in every batch or bag of popcorn we enjoy, there are always those pesky kernels that don’t successfully pop that we deem the failures of the popcorn world. And if they do pop, they crack open without fully popping and are just as bad as the rock-hard kernels because they deceive us into thinking they’re a fully popped piece of popcorn.

There are several reasons why this happens, and no it’s got nothing to do with karma. A few missing links in the formula used when popping are usually the culprit.

The most common cause is a faulty hull. If it’s got a small crack or is compromised in some way the correct pressure does not get built up to enable the full kernel to pop. So the moisture we talked about earlier that is essential to completing the process, heats up and turns to steam that leaks out of the kernel.

Low moisture content can also cause the kernels to not pop, if not enough steam is built up, the pressure doesn’t build up correctly and the starch inside cannot gelatinize.

Improper heating of the kernels can also be the problem because corn will pop best in dry heats that are fully produced by air or oil. This heat surrounds the kernels and heats them evenly throughout and fast too. Heating them too slowly or at temperatures that aren’t high enough can throw this balance off and not create enough pressure. So essentially it’s all about the pressure.

How To Get The Perfect Pop

So, the amount of moisture inside the kernel turns to steam when the kernel is heated, the pressurized environment that’s created by the hull gelatinizes the starch transforming it from a solid, into a soft, malleable form. Meaning that the kernel can be shaped easily because of how soft it has become.

This pressure eventually exceeds how much the hull can withstand and it ruptures. This process creates a perfectly popped piece of popcorn that has successfully triumphed over its failure peers.

Why Do They ‘Pop’?

That famous popping sound is what makes us love popcorn so much, besides the delicious tastes that it has within. The popping sound is actually the pressure building up because of the moisture inside turning into steam, and then when this pressure bursts, that ‘pop’ occurs.

Final Thoughts

So, we’ve learned about the full process involved in getting the perfect popcorn piece and how they can result in failed pieces. It’s a combination of the perfect amount of heat, pressure, and timing to create the pieces and when one or more of these things is thrown off balance or unsuccessful, the kernel just simply droops and fails all our expectations.

We’re really bashing into those poor unpopped kernels, aren’t we? Maybe next time we find the pesky tooth-breaking kernel pieces inside our popcorn, we’ll have more empathy for them.

Frequently Asked Questions

What Causes Popcorn to Explode?

The moisture inside the kernel hull layer turns to steam when heated at the correct temperature causing it to expand rapidly.

The starch that protects this water turns into a jelly-like substance and as the kernel continues to heat the pressure exceeds its capacity and the kernel opens. During this process, the starch inflates and then cools quickly, creating popcorn.

How Big is a Piece of Popcorn When Popped?

A successfully popped piece of popcorn is around 20 to 50 times bigger than its original kernel shell. However, if it is heated too slowly or the pressure is off, it will not pop causing the steam to leak out of the hull and resulting in a failed kernel piece.

Why Does Popcorn Pop When It’s Cooked?

The popcorn kernels contain oil, starch, and moisture that are surrounded by a hard coating. When the kernels are heated, this moisture inside the kernel attempts to expand into steam but is unable to escape through the hull coat.

When it finally bursts, that famous popping sound that we all associate with popcorn occurs. Resulting in a perfectly fluffy piece of popcorn. Repeat this a hundred times and you’ve got yourself a batch.