Microwaves

• Microwaves are extremely high frequency radio waves and can be reflected, transmitted or absorbed by anything in their path. As explained by the U.K. Portable Appliance Testing (PAT) Organization, metals reflect microwaves; glass and plastic materials are partially transparent and allow microwaves through. Anything which contains moisture such as food (and indeed humans) will absorb microwave energy.
  
  

Microwave Cooking

• David E. Hintenlang, associate professor nuclear and radiological engineering at the University of Florida at Gainesville, explains that microwave ovens cook because the energy absorbed causes water molecules in the food to vibrate. It is friction between the molecules that results in heat generation.
  
  

Nutrients

• However a food is cooked, some vitamins will be lost or degraded, and the longer the exposure to heat the greater the loss. Vitamins B, C and folic acid are particularly heat sensitive. As microwave cooking is short, vitamin loss is generally small compared to boiling. Quoted in the New York Times, scientists at Cornell University found that almost all the folate in spinach was retained when cooked in a microwave oven, compared to a loss of 77 percent when boiled.
  
  

Benefits

• Cooking vegetables conventionally results in a loss of nutrients into the cooking water. An example is broccoli, which loses gluosinolate, a sulfur-containing compound that may have anti-cancer properties. Researchers at Cornell found that bacon cooked in a microwave had lower levels of harmful nitrosamines than some which had been conventionally cooked.
  
  

Food Safety

• Cold spots can occur while microwave heating, unless the food is stirred and rotated through the cooking process. Where food is not adequately cooked through, bacteria can survive and multiply, leading to the possibility of food poisoning. It is important to follow cooking instructions on food packaging.
  
  

Considerations

• The microwaves generated only exist once the power is on. Turn the oven off and generation ceases. Microwaves do not remain in food and cannot make the food radioactive. If a microwave oven is damaged, PAT recommend not using it until an experienced technician has checked for leakage and declared the oven safe to use.