Microwave oven

A microwave oven is a kitchen appliance employing microwave radiation primarily to cook or heat food.

Safety and controversy

Microwaving food is fast and popular, but there are potential hazards. See also: Microwaving.

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Uneven heating

Food is heated for so short a time that it is often cooked unevenly. Microwave ovens are frequently used for reheating previously cooked food, and bacterial contamination may not be killed by the reheating, resulting in foodborne illness. The uneven heating is partly due to the uneven distribution of microwave energy inside the oven, and partly due to the different rates of energy absorption in different parts of the food. The first problem is reduced by a stirrer, a type of fan that reflects microwave energy to different parts of the oven as it rotates, and by a turntable that turns the food. The second problem must be addressed by the cook, who should arrange the food so that it absorbs energy evenly, and periodically test and shield any parts of the food that overheat.

Related Topics:
Bacteria - Foodborne illness - Reflects

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Acute dangers

Liquids, when heated in a microwave oven in a container with a smooth surface, can superheat; that is, reach temperatures that are a few degrees Celsius above their normal boiling point without actually boiling. The boiling process can start explosively when the liquid is disturbed, such as when the operator grabs hold of the container to take it out of the oven, which can result in severe burns. A common myth states that only distilled water can exhibit this behavior; however, this is not true. http://www.amasci.com/weird/microexp.html#myth

Related Topics:
Superheat - Explosively - Distilled water

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Closed containers and eggs can explode when heated in a microwave oven due to the pressure build-up of steam. Products that are heated too long can catch fire. Manuals of microwave ovens typically warn of such hazards.

Related Topics:
Egg - Steam

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Tin foil, aluminium foil, ceramics decorated with metal, and products containing other metals can cause sparks when they are used in a microwave (some find it entertaining to place a compact disc in a microwave for this reason, however this may produce toxic fumes, not to mention destroying the CD in a circular mesh pattern). Microwaving small, smooth, solid metal objects without pointy ends (for example, a spoon) can sometimes be safe, and usually does not produce sparking. Forks, however, will readily produce sparks when placed in the microwave. This is because while it acts as an antenna, absorbing microwave radiation just like other metal objects such as the spoon, the pointy ends of the fork will act to concentrate the electric field formed at the tips. This has the effect of exceeding the dielectric breakdown gradient of air, about 3 megavolts per meter (3X106V/m), causing sparks to form. This effect is directly analogous to the effect of St. Elmo's fire. The formation of sparks on sharp metal objects may be prevented by placing the untensil in some food or liquid while in the microwave, as this has the effect of preferentially conductively dissipating the charge before the electric fields can build to the point where they exceed the breakdown value of air. Finally, as mentioned previously, any metal or conductive object placed into the microwave will act as an antenna, and its electrons will thus be thrashed back and forth through the object (a high frequency alternating current) causing some ohmic heating to occur. The extent of this heating effect will vary depending on the size, shape and conductivity of the object. Several microwave fires have been noted where chinese takeout boxes with a metal handle are microwaved, and also where "homemade" microwave popcorn bags have been sealed using a metal staple, which is then heated and sets fire to the bag. This type of accident can pose an exceptionally dangerous situation because of the extremely flamable airy mixture of popcorn and oil in the bag. Thus, as a general rule, it is good practice to remove any metal utensils or metal containing objects from a microwave oven before operating it, as the behavior of these objects when immersed in a strong microwave radiation field is often unpredictable at best.

Related Topics:
Tin foil - Aluminium foil - Compact disc - Electric field - Dielectric breakdown - Megavolts - Meter - St. Elmo's fire - Antenna - Alternating current - Ohmic heating - Popcorn - Oil

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Controversial hazards

Radiation

Some people are concerned with being exposed to the microwave radiation. The USA legal limit of leaking radiation is 1 mW/cm2 at 5 cm from a new oven (for a used oven, it is 5 times higher). It is rare for an oven to exceed these limits. As a comparison, a GSM cellular phone may emit up to 1 W at 1800 MHz, which is 2 mW/cm2 at 5 cm. Whether or not cellular phones are hazardous to the health is also controversial.

Related Topics:
GSM - Cellular phone

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It is a common myth that metallic kitchen equipment, like kitchen forks and knives, can somehow repel the microwaves back into the magnetron and cause it to catch fire. This is highly unlikely. See microwaving for more information.

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Food

Some people claim that there exist more subtle dangers than the ones listed above associated with cooking in a microwave oven. Namely, they often claim that microwave cooking causes more loss of nutrients than conventional cooking and that microwave radiation leads to chemical reactions in the food that are different from those occurring during conventional heating and which can cause cancer or other ill effects if consumed. There is no accepted scientific validity to these claims, and most scientists and skeptics consider these claims to be alarmist and pseudoscientific. Here are some anti-microwave websites:

Related Topics:
Skeptics - Pseudoscientific

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• Microwave Cooking is Killing You!
• Do You Microwave Your Food?