Introduction - In process of writing as of 28 October 2012 Armchair (discuss • contribs) 17:20, 28 October 2012 (UTC)
Many kitchens make use of microwave ovens. In the view of most, their scope is more limited than ovens that use direct heating; that is, gas and electric ovens. However, that said, there are many of them in use, and for a restricted set of tasks they are useful, allowing as they do shorter thawing, heating, and cooking times than might otherwise be expected. These notes will attempt to summarize their obvious uses.
- Microwaves (extra high frequency radio waves) are used to heat the food in such ovens, and they most often deliver a maximum of between 600 and 1000 watts of energy, with adjustments for time duration and energy output. The energy is safely contained within the oven by a reflective metal box; that is, the internal panels of the oven. Because thin metallic films and meshes also reflect microwaves, see-through doors become possible without any danger.
- Uncontrolled microwaves could also cause burns to people, so a high standard of safety is applied, ensuring that there is negligible leakage and that safety interlocks prevent the generation of microwaves whenever the door is opened. These safety features are tested for all new products, though there are rarely any compulsory tests for ovens after the point of sale.
- Microwaves heat by moving water molecules, so foods that contain significant water content are obvious choices for their use. Examples include the heating of milk in baby bottles, the making of sauces, and the heating of certain packaged foods. Closed foods like eggs in their shells cannot be cooked with microwaves since expansion of the contents might cause the egg to explode. So also with the baking of potatoes unless their skins are first pierced several times. Because effective heating takes place only in the first one or two inches (5 cms) of the food; deeper cooking is achieved by the continuous conduction of heat from the areas of absorption and the periodic stirring of the contents by the cook.
- Microwaves alone cannot properly brown food, so additional items are used to do so. To make food crisp on its surface, a special plate that is made hot by microwaves is used to hold the food: for example, for bacon, pizza, and to finish 'roast' potatoes. To attain browning of a more general kind (grilling), say for a gratin, the addition of direct heating elements or hot air jets can be used. For those foods that need continuous moisture while they cook, plastic steamers are used.
- Metals in any amount reflect microwaves, so the containers used during cooking must be transparent to microwaves; that is they are made of materials free of significant traces of metal. Many existing glass and china kitchen items work well in microwave ovens, and some of these are marked as Microwave safe. Heating a cup of water (to avoid overloading) along with a dish that is to be tested for suitability, will result in hot water and a cool dish if the item is useful for the microwave, but the dish will be hot if it is not. Note that containers for microwaves might still not survive air jets and grills, so care is needed in their use. A common lid for dishes is a pierced plastic film, some brands of which are more suitable for high temperatures than others.
Types of Oven
- Solo microwave ovens: These have a single microwave function and are usually adjustable as to their output and timing. The most common items have a maximum output of between 600 and 750 watts. In addition to output the size of the microwave can be quoted as to its cubic capacity; a fairly large capacity is about 31 litres, but there are many smaller sizes, and a certain amount of the capacity is unavailable for cooking, it being taken up by the rotating turntable.
- Combi microwave ovens: These combine a grilling or browning feature that can work alone or in combination with the normal microwave function. The feature can consist of direct heating elements or heated air jets.
- Sensor microwave ovens: These can be basic or combi, and include automatic weighing of the food contents, so in conjunction with knowledge of the food type, taken from a selector dial, the cooking or thawing time can be worked out automatically. The sensor technologies are still being developed and new ones appear from time to time.