This is NPR's Life Kit. I'm Alison Aubrey.

We hear a lot about calories. They're printed on labels and menus,

and we're told if you want to lose weight, you got to eat fewer of them.

But if you ever stop to think, what is a calorie?

Well, the best way to find out involves getting out of blowtorch.

There's anything that we chemists know how to do. It's burn things.

That's Matt Harding's. He's a chemistry professor

and we're in his lab at American University.

He's got the technical definition of a calorie.

The calorie is the amount of heat required to raise

the temperature of one gram of water, one degree Celsius.

But what does that really look like?

So what we're going to do is we are going to burn our food.

You ready? Yes. Okay.

We've got two different foods here. A piece of white bread and a handful of

little wheat kernels. So I've got my propane torch here that we're

going to use to start this bread the way it needs to be going.

All right, let's do it. We need to measure how much heat each

piece of food gives off. That's where the calorie count comes from.

Now you see the smoke coming up from in there?

Oh yeah, look at that flame. That's a lot of smoke.

It is a lot of smoke. These things are reacting with oxygen or

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