When microwaving a bag of popcorn, why doesn’t the first kernel that is popped burn by the time the last kernel is popped?
In: Chemistry
Kernels burn because they get too hot.
They get too hot because they get so much heat.
They get so much heat from water vapour.
Water vapour comes from exploded kernels and inside.
Exploded kernels help accelerate the rise in temperature outside as their water vapour is dissipated amongst all (neighbouring) kernels.
There is very little water vapour outside the kernels initially. All of it is inside.
Only the water inside the kernels can heat up due to the microwave.
Liquid water can only get to 100 deg C. Water vapour is not limited in temperature.
When there’s a lot more water vapour around as most kernels have opened, the outside temp can get very high and either directly burn opened kernels or the little butter/oil that was added for taste also starts heating up and burns them from below.
That’s why, Eli.
The water vapor from popping kernels is a big part of it. If you microwave it for long enough that the water vapor all escapes, the popcorn will in fact begin to burn – ask anyone who works in an office!
The process of popping a kernel absorbs more energy than it releases. When there are still lots of un-popped kernels, so much heat energy is absorbed by all these kernels that it prevents the temperature of the oils and steam in the bag from rising to the point where an already popped kernel would burn. Once most of the kernels have popped, the heat energy has nowhere else to go and the temperature goes up, eventually burning the popped ones.
This is why it’s almost impossible to get all the kernels to pop without burning some of them.
It takes a certain amount of energy to burn popcorn. It takes less energy to pop it.
As long as there are unpopped kernels, the energy will go into popping them before it will begin burning the others.
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Good question.
Microwaves heat up different things differently depending on how they absorb them. That’s why some containers are microwave safe and some will melt if you put them in.
Water absorbs microwaves really well, that’s what heats up when you microwave something mainly…that’s why it has a funky texture when it cools down. All the water is boiled out of it.
Kernels pop because they have moisture inside them and when it heats up it builds up pressure and that is what makes them pop. Once they pop they heat slower because the water is gone though. You can still burn them if you go too long though.
A lot of the answers miss the fact that only a small patch in the middle of the bag is catching the majority of microwave energy, converting it to heat. The kernels don’t see much of it, despite moisture content.
As the kernels pop, they become less dense and float towards the top of the pile, while the unpopped ones generally fall to the bottom (where the heat patch and oil are). If left too long, it is the popped kernels nearest this patch that may burn first, along with some of the outliers at the corners of the bag.
Just wanted to add that a bag of microwave popcorn actually has a metal layer in the bag. That is why it says to only put it a ceran way.
The metal layer getting really hot helps the popcorn pop.
After a certain amount of time the metal layer actually gets so hot it will burn the popcorn or maybe even start a fire.
If ever notice, a bag that only got a tiny bit burned, the burned popcorn is from the side of the bag that was down.
It wouldn’t happen if you just put a spoon popcorn kernels in the microwave.
Once they pop they don’t really absorb any more energy from the microwave.
They only burn if there is a hot metal layer underneath them.
Why do they do that?
Well it helps transfer heat and helps it pop up really fast.
The downside is you might make your entire house stink really bad if you cook it too long.
I recommend hot air poppers, or if you like to cook,. Do it the old way
Coconut oil is awesome, any oil works.
Do the 2 spoons of oil and a 1/4 cup of popcorn into a pot with a lid.
Takes 5 minutes, way more tasty.
I like olive oil and sea salt and some black pepper.
Microwaves are really good at heating water. Dry things don’t heat very well compared to wet things.
When you start microwaving a bag of popcorn, almost all the moisture is inside the kernels, and so they absorb the microwaves and kernels begin to heat up. A kernel pops and becomes popcorn.
Microwaves continue to be absorbed by the kernels full of moisture. The dry popcorn is largely unaffected. Kernels continue to pop.
Eventually there are almost no kernels left, they have all popped into popcorn. Their moisture was effectively protecting the popcorn by sucking up all the microwaves, but now there are almost no kernels full of moisture to suck up the microwaves, and instead the popcorn is sitting in a cloud of super-heated vapor. The popcorn begins to burn
Microwaves are effective at heating water. When the miniscule amount if water in the kernel flashes to steam, and explodes, you are left with a dryer popped corn.
It will still burn, but most of the energy is being absorbed by the water aka, the unpopped kernels
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