Metal, we are told, should never be used in a microwave. Yet that is exactly what the oven is made from, right down to the reflective mesh in the window.

So what's the big deal?

To understand the relationship between microwave ovens and metal, it helps to know a little about how these modern cookers work. Most people who own one are already aware that the oven itself never heats up; so how does it cook food?

The answer lies in the power source, which is a device called a magnetron. This bombards the interior of the oven with electro-magnetic waves similar to those found in sunlight. These 'microwaves' bounce off the metal sides of the oven, as well as any other metal object placed in their path.

In the course of doing this, they will pass through any non-reflective containers and agitate the water, fat and sugar molecules of any foods they find there, thus beginning the cooking process. And therein lies our first clue.

If the waves bounce off metal, it should be obvious that any food inside such a container will remain unaffected and therefore will not cook