If you regularly pop your own popcorn, you will have noticed that some of the kernels don’t pop. If you keep heating the kernels hoping for the stragglers to explode, you end up scorching the already popped corn. Well, no matter what anyone tells you (I’m looking at you, America’s Test Kitchen) there is no fool-proof method to ensure that all the popcorn kernels pop. Sure, many variables affect how many of the kernels pop, but some of them may never pop. Period. That’s just…physics.
You may already know that popcorn explodes when heated because there is water inside the kernel. When this water heats up and turns to steam, a lot of pressure is created inside that little kernel. It’s like a sealed water bomb! Eventually, it just explodes. But unlike a bomb, it fluffs up into a tasty snack.
Popcorn is not the only grain that has water trapped inside. This same principle enabled Alexander P. Anderson to develop the first puffed breakfast cereals with his “food cannon.” Other grains require a bit more finagling than popcorn to puff up.
You now that water starts to boil at 212° F, turning to steam. When the water is heating up inside the waterproof popcorn kernel, the kernel becomes a pressure vessel so the water continues to get hotter and the steam builds up until the hull finally explodes.
There are many variables that affect how well your popcorn pops. Trying to pop too many kernels at once will lead to a lot of unpopped kernels. Using dry air, hot oil, or the microwave could all lead to different popping rates.
One variable you can’t control is how much water is inside the popcorn kernel. Popcorn kernels can dry out over time. The hulls can also become compromised, leading to water loss.
Too Little Water In Popcorn Kernel
A dried-out kernel with too little water will never pop because there is not enough water to cause sufficient pressure inside the hull to cause it to puff up. A kernel with a compromised hull will not allow the pressure to sufficiently build up in the first place, even if there is enough water. It’s allowed to escape as the kernel heats instead of being released all at once. It is estimated that a popcorn kernel needs 12 to 14% water to pop. Anything less and it fails.
Too Much Water in Popcorn Kernel
Confusingly, the kernel will also fail to pop if it has too much moisture! You’d think more water would just make more bang. But an overmoist kernel will be soft to begin with. You can test this with your thumbnail, in fact. If you can make a little dent in a kernel, it’s too moist.
These watery kernels will not puff up but may become a disappointing watery and dense piece of popcorn, like a little sphere. You may have encountered these before…they appear often in Cracker Jacks (cheap, low-quality popcorn).
While the heat and steam are building up inside a viable kernel, the starches in the grain gelatinize. If there is too much moisture, steam expands too quickly, not allowing enough time for the starch to gelatanize. Without this, the fluffy popcorn can’t happen. Such a kernel is a dud, like a firecracker that just fizzles instead of exploding.
Can You Get Them to Pop?
These kind of unpoppable kernels are called in the trade “Old Maids” or “Spinsters” for reasons no one seems to know. But some folks can’t take the word “unpoppable” for an answer and dream up all sorts of methods to get the kernels to pop, like soaking dry kernels in water or trying to dry out over-wet kernels. To me, this is like learning to juggle. It’s probably doomed to failure unless you have a whole lot of disposable time.
You will probably have better luck learning to juggle, in fact because as far as anyone knows, those defective kernels are never, ever going to pop.
If a whole lot of your kernels don’t pop on a regular basis, there may be problems with your popping method. Don’t try to pop too much at once, for starters. You could also be buying low-quality popcorn.
I can tell you not to fall for any “heirloom popcorn” jazz. What you’ll get for the extra money is more unpopped kernels and popcorn that is dense and chewy instead of light and fluffy. Older is not better with popcorn. Today’s modern cultivars are bred for better popping.
