why does popcorn seem to pop at a somewhat consistent rate regardless of the amount, instead of all of them popping closer to at the same time?
In: Physics
Popcorn has a few layers. A core of water surrounded by starch and then a harder outer shell. The way popcorn pops is that water begins to boil and causes the kernel to explode. All of the kernels will get to the point where the water is expanding at slightly different times based on how the kernels are being heated, as well as how hard the starch/shell is in comparison to other kernels.
The corn pops when pressure from the internal moisture boiling gets too high for the strength of the hard outer shell. There is natural variation from kernel to kernel in how much moisture there is, and how thick/strong the shell is, plus possible weaknesses/defects in the shell, plus uneven heating from whatever you’re using to heat the kernels in. Add all of those factors together and you get a wide range of popping times. Thin-shelled high-moisture kernels that happen to pass through a hot spot in the microwave are going to pop a long time before drier, heavy-shelled kernels passing mostly through cool spots in the microwave. Of course, the vast majority of kernels will lie somewhere between these two improbable extremes – so you get roughly a [normal distribution](https://getnave.com/blog/wp-content/uploads/2018/08/frequency-distribution-types-normal-distribution.png) (bell curve) of popping times, with middle-length times being the most common. You usually get a few early pops, then a faster popping region, then a few late pops again slower.
Side note: Things that depend on many variables, with an element of randomness, often end up looking like a bell curve. The classic example is test grades. The kids that are naturally smart AND study hard AND correctly guessed what’s on the test do super well. The not-smart kids who ALSO don’t work hard AND didn’t know there was a test that day do super poorly. However most students are some middle combination of those factors not either extreme, so you get a bell curve shape, with [middle-ground grades being more likely for most people](https://community.alteryx.com/t5/image/serverpage/image-id/70245i5975B12143193352?v=v2).
It is the same as boiling water. Boiling water consumes energy and energy is supplied at a consistent rate, so water also boils at a consistent rate. Popping a popcorn is basically boiling water inside the shells. The high pressure of water vapor causes the the shells to pop.
Imagine if all the kernels popped at the same time though? Lol you’d pres start on the microwave, wait like a minute, then a crazy loud bang, then think to yourself “Ooo it must be ready”. I’m sure I’d still find a way to burn some
I’d say it’s more like a bell curve rate, once it gets going it peaks and then starts to reduce popping. This makes sense statistically. Around the peak of the bell curve the heat is about right for most to pop, but there are outliers either way who pop earlier or later due to factors like moisture and size
I’ll add something because it hasn’t been mentioned yet. Your microwave produces a frequency that interacts best with water. Most other molecules it either goes through or bounces off. So the first layer of water will keep absorbing the energy. This is why you have some parts of food molten hot, and others still frozen.
This isn’t a huge issue for popcorn, because of the kernals and how the bags are designed. But it does add some variance to when some kernals are heated.
You can make them pop all at once like this: https://www.youtube.com/watch?v=Ta5jh9VglDw
Microwaves and pans and even air poppers don’t heat in a completely uniform manner so each kernel will make it to the “popping point” at different times. Microwaves are really notoriously bad at heating things uniformly and are therefore probably one of the worst ways to pop some kern. A quarter will be un-popped and a quarter will be burnt, leaving a half bag of semi smoky smelling corns.
The simple answer is this. Only the bottom layer of kernels is contacting the hot thing. Whether it’s the pan on the stove or foil liner in the microwave pack. Once a kernel pops it floats to the top and new unpopped kernels sink. That’s also why it doesn’t burn until almost all the kernels are popped.
They do, you are just noticing the details. Speed it all up considerably and it would sound more like what you are expecting.
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