Microwave Magic

What is just about the one kitchen gadget that most households have? If you read the title of the post and guessed microwaves, then you're right!  But, do you actually know how your microwave works? Or is it just a magic box you put cold stuff in and hot stuff comes out? Let's talk a little big about how microwaves work.

Photo owned by Modernist Cuisine. (You didn't think I had a machine shop to make this, did you?)

The photo above shows a microwave that has been cut in half. On the left we have the chamber where you put your food. On the right is a device called a magnetron. (Tell all your friends you have a magnetron and watch them be afraid!) The magnetron uses a transformer to create microwaves, which are a type of electromagnetic radiation. As shown by the white arrows above, the waves propagate (fancy word for move) into the path of a fan, which disperses the waves throughout the chamber and thus heat your food by irradiating the molecules. The word "radiation" generally scares people a bit, so let me be clear: MICROWAVING YOUR FOOD WILL NOT MAKE IT RADIOACTIVE. Well, not any more than it already is. But that is for an advanced physics course to explain. The second thing that is concerning about radiation is that being exposed to it can cause cancer and other health problems. Microwaves are a type of radiation; however, they are contained in the microwave (the cooking device) in a very interesting way.

The most common type of radiation that people generally think of being concerned about is called gamma radiation. Gamma radiation is a very small wave that is so fast that it can pass right through solid objects and scramble their atoms, thus causing the health problems. Microwaves are much, much bigger than gamma waves, and thus can be contained. Gamma waves are about 10^-12 meters long. Microwaves are a few centimeters long. So containing microwaves is relatively simple. The screen door on the front of microwaves are usually plastic with some sort of grating on the front. We don't have to worry about being irradiated because the holes in the front of the microwave are so small that the waves inside are too small to get out! How cool is that? The holes are big enough that we can see through them and watch our food, but small enough that it protects us from the harmful radiation within.

This is a lot of complicated physics, so I did a little experiment that you can do yourself to show how big microwaves are. *Please note that the idea for this belongs to Modernist Cuisine and I have simply repurposed it for the use of showing a concept. All of the pictures are my own.*

First, I cut 10 cubes of cheese out of a block of sharp cheddar (good stuff) and made each subsequent block smaller than the first. I ranged the cubes from about 1in^3 to REALLY REALLY TINY.

On the right we see the REALLY REALLY TINY cube.

Below you see that I arranged them on a plate in a circular fashion so that as the base of the microwave rotates, all of the cheese is affected evenly.

Awww aren't they so....cube! (It's a pun on cute, just FYI).

Then, I put the plate with the cubes in the microwave for 10 seconds. And here's what I found:

Wait....what?

The three largest cubes melted the most, while the small cubes...did nothing. For posterity's sake, I put the plate in for another 10 seconds:

Here are the five smallest cubes...apparently unmelted. They were also quite cool to the touch. But what happened to the big ones?

Here we have....some large puddles of melted cheese. A quick thermometer test said that the melted cheese had reached a temperature of 114 degrees fahrenheit, while the little cubes were room temperature.

So what the heck happened?! The average home cook would shrug their shoulders and eat their melted cheese happily. But us molecular gastronomists demand answers! The answer is in the physics. The microwaves, as we said before, are a few centimeters in length. Half of the cheese cubes were smaller than that, so it is impossible to warm them with microwaves. They're too small to be warmed. If you've ever tried to make chocolate fondue or chocolate dipped strawberries, you usually put chocolate chips in a double boiler. A novice puts a big bowl of chocolate chips in the microwave and it takes FOREVER to warm them. Why? Because each chocolate chip is too small to be affected by the microwaves, so it has to warm the whole bowl rather than each individual chip; it's the same principle. So, the moral of the story is don't put small pieces of food in the microwave--it just won't work.

Liked this post? Let me know in the comments! Any and all questions are welcomed and accepted!