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 - or at least will only cook very slowly. This phenomenon can actually be used to the cook's advantage.
By wrapping parts of unevenly sized food particles in baking foil - for example, the ends of chicken legs - we can slow down the rate at which these cook and produce a more even finish. Of course, when doing this it's important to ensure that the foil does not touch the inside surfaces of the microwave and cause electrical arcing. While this may not be harmful to you, it could be lethal as far as the oven is concerned.
Food can also be cooked in shallow foil containers, with the same proviso as before; these must not be allowed to touch the interior surfaces of the oven. With these, the effect is for the food in them to be cooked from the top down, with practically all the heating of the bottom layer taking place through convection. Again, the crafty cook uses this to advantage.
When the bottom of any metal container used in this way feels hot, it follows that the food sitting on top of it must be at the same temperature since that is what is providing the heat. There is no need to guess. To sum up, contrary to popular belief and some uninformed comment, metal can be used in a microwave providing it is used sparingly and with caution.
Most often you will not want to use it at all for the reasons given above, but just occasionally it can be your staunchest ally.
Michael Sheridan is an acknowledged authority and published writer on cooking matters. His website at http://www.all-about-cooking.com contains a wealth of information, hints, tips and recipes for busy home cooks.