When I was a teenager, my choice of food was basically determined by three criteria:
- It needed to be ready in under 10 minutes.
- It needed to have enough calories to make me not hungry anymore.
- And it needed to be (marginally) edible.
That was really it. And so it won’t surprise you to know that a portion of my diet at the time consisted of — you guessed it — Hot Pockets. And to be fair, they don’t actually look so bad on the box.
For those of you who don’t know, a Hot Pocket is a frozen Pop-tart filled — instead of with fruit — with nasty meat and sauce. You’re supposed to stick it in a microwave for a few minutes and let it cook/heat, and then it’s supposedly edible. But it never actually is. They always come out looking like this:
They’ve even had to redo their entire advertising campaign, after a (really funny) comedian so eloquently explained the entire problem with Hot Pockets.
“Is your Hot Pocket cold in the middle?”
“It’s frozen. But it can be served boiling lava hot.”
“Will it burn my mouth?”
“It’ll destroy your mouth. Everything will taste like rubber for a month.”
This is a problem — not just with Hot Pockets — but with many microwaveable frozen things. Either you can heat the outside to a normal temperature and the inside will be frozen, or you can heat the inside to a normal temperature, which requires the outsides to boil. Either way, you lose.
But why? What’s the physics behind this? Microwaves are just a type of electromagnetic radiation, like visible light, infrared radiation (commonly called heat), and radio waves. But microwaves are special because they are just the right wavelength to be absorbed by fats, sugars, and water. The water — in particular — does something special. Water molecules are very simple, with an electronegative oxygen atom and two electropositive hydrogen atoms.
You bombard these molecules with microwaves, and the microwaves cause the water molecules to rotate.
Rotational motion is a form of energy, and that excess energy causes the water to heat up! But there’s a difficulty for your frozen Hot Pockets. You see, the water molecules aren’t free to move.
They’re bound in crystals! On a molecular level, they bind together like this:
Which means that microwaves don’t heat ice, not nearly as efficiently as they heat water! (Thanks to Michael Broide for showing me about this phenomenon.) The outermost layer of your frozen food has just been exposed to air, so some of those crystals have started to melt. That outer, watery layer can heat up quickly. But all the layers inside are lousy at absorbing microwaves!
So the outer layer has to get hot enough to melt the ice crystals in the next layer. Then that newly-melted water can heat up and melt the ice farther in. In the meantime, however, the outermost layer gets really hot! And that is why Hot Pockets can both destroy your mouth and be frozen on the inside at the same time!