Do microwave ovens heat food from the inside?

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

14 May 2006

A reader who would like to remain anonymous asks: is a microwave better than a kettle? And is it true that microwaves heat food from the inside? How do they do that?

“Better” is a vague word. The microwave is more efficient in heating water, but it is slower than a kettle. That is, it uses less energy to boil some water but it takes more time to do the job. So which of the two is better? Well, that depends on what you need to do with it.

Nevertheless, even though it is more efficient, many people find that their electricity bills increase when they buy a microwave oven. The reason for that has more to do with a change of lifestyle than with the science of energy utilisation inside the appliance…when your tea cools down a little, you can easily heat it up in the microwave without having to pour it into a sufuria. You pay for that convenience with a higher power bill. Without the oven, you’d probably drink the cold tea, anyway!

But does a microwave heat food from inside? Yes and No. If heat a mandazi in this oven, does it get hot at the centre while remaining cold on the outside? No. But if you boil water in a cup, the cup doesn’t get very hot even though the water is boiling. This is probably the reason why many people believe that the microwave heats things from inside.

The microwave oven works by shining electromagnetic waves on the food. The term “electromagnetic wave” is just a sophisticated way of saying radio waves, or light! The radiation used is of a frequency that is mainly absorbed by water and, to smaller extent, cooking fat and sugar. However, plastic, glass and ceramic materials are virtually unaffected by the microwave radiation.

When the electromagnetic waves are absorbed in water, they rotate its molecules very fast (about 2.5 billion times per second) thereby generating heat. Thus if the water is in a cup, the liquid will heat up before the container. So, in a way, one can say that the heating is from the “inside”…but that doesn’t mean that the central area of the food heats up before the outer parts.

Despite its convenience, many people have fear using a microwave thinking that it is unsafe. I have heard some arguments that this device uses dangerous waves which can kill if consumed in large quantities. That is a fallacy. It is not possible to eat the waves – have you ever tried to eat light?

The only danger is if the waves leaked from the oven compartment. They can burn the skin just like boiling water in a sufuria. But the risk of that leakage is much less than that of gas leaking from the cylinder and causing a fire in the house.