How does a microwave work?

March 9th, 2012

Appliance Talk Microwaves

There’s no doubt that microwaves have revolutionised the kitchen. From re-heating leftovers (“zap it in the microwave”) to meals in a minute, the ease and efficiency of microwaves has seen them become an ubiquitous kitchen appliance.

But how does a microwave work? How does it heat and cook ten times faster than an oven or a cooktop?

The oven’s namesake, microwaves, are a type of radio wave that specifically affects water molecules. They are produced by a magnetron.

The magnetron

The radio waves make water molecules move around very quickly and it’s this movement, this friction between water molecules, which creates heat.

This is why only substances with water in them get hot in a microwave, and why plates, cups, or dry rice for example, won’t cook.

It’s also the reason that food in a microwave cooks evenly. When people say that a microwave cooks from the inside out they are referring to the difference with convection heating where a direct heat source (the element or fire) cooks directionally.

Microwaves have metal walls in the inside so that the electromagnetic energy stays within the enclosure and doesn’t escape and cook us! After all, we’re made up of 70 per cent water.

Operating an empty microwave will have the same result as putting a metal object, such as fork, inside of it. The microwaves can’t be absorbed into anything and so they will reflect off the metal walls, or object until sparks fly – an obvious fire risk and a no no.

What is super heating?

Food, liquids especially can be super heated. This means that water won’t necessarily boil when it reaches 100 degrees. Super heated liquid will bubble when it is moved or when something like a spoon or tea bag disturbs it. Some microwave makers suggest letting microwave-heated liquids stand for 30 second before moving them.