how in a microwave food is cooked?

Answer 1

A microwave oven uses microwaves to heat food. Microwaves are radio waves. In the case of microwave ovens, the commonly used radio wave frequency is roughly 2,500 megahertz (2.5 gigahertz). Radio waves in this frequency range have an interesting property: they are absorbed by water, fats and sugars. When they are absorbed they are converted directly into atomic motion -- heat. Microwaves in this frequency range have another interesting property: they are not absorbed by most plastics, glass or ceramics. Metal reflects microwaves, which is why metal pans do not work well in a microwave oven.

Answer 2

Microwave cooking is a safe and quick way to prepare food. Many dishes are extremely adaptable to microwave cooking, while others are not. Knowing how to cook common foods will vastly improve results.

Microwaves are high frequency electromagnetic wave, very similar to regular radio waves. However, microwaves are much shorter, less than 3 inches long, contrasted to radio waves which vary in length from 3 feet to several miles. The microwaves are contained within the microwave due to the construction of the oven and due to the fact that microwaves are very short in length. The microwaves are produced in the magnetron unit and enter the oven cavity through an opening in the metal interior of the oven, usually through the top.

A fan will distribute the microwaves throughout the oven. Since microwaves cannot penetrate metal, the energy is contained within the oven, does not leak out and will bounce off the metal sides inside the oven cavity at right angles There must be food or water in the oven while it is operating to absorb the energy and to prevent the microwaves from damaging the magnetron unit.

Although the microwaves cannot penetrate metal, they can penetrate paper, plastic, glass, and pottery. Therefore, food should not be cooked in regular metal pans, but can be cooked in paper, plastic, glass, or pottery, which do not have metal trim or glazes. Newer microwave ovens will tolerate some metal, so check the operating handbook to learn what is apporpirate for your microwave oven.

Microwave energy cooks food by friction rather than the more conventional way of cooking by conduction, convection, or radiative heat transfer. The water molecules in food are randomly orientated within the food; the positively charged hydrogen atoms and the negatively charged oxygen atoms are not lined up.

When an electric field such as a microwave field is present, the water molecules will rotate to orientate themselves to the field. The positively charged hydrogen atoms will point towards the negative end of the field and the negatively charged oxygen atoms will point to the positive end of the field. As the polarity of the field changes, the water molecules will rotate to reorientate themselves to the positive and negative end of the field.

The polarity of the field changes at a rate of 2450 MHz (2.45 billion times per second). The water molecules will rotate to maintain their alignment. This rotation causes friction between the water molecules and producing heat which cooks the food. The vibration continues only as long as the microwave oven is operating, but the heat from friction will continue a short time after the oven has been turned off.

Microwaves do NOT cook food from inside out contrary to the popular misconception. Microwaves do penetrate the food from every direction, top, bottom and all sides, from 3/4 to 1 1/2 inches. In doing so, no chemical changes occur in the food. The vibration of the food molecules causes heat in the outside areas of penetration and these areas begin to cook. As outside areas cook, the heat generated will be conducted to parts of the foods not touched by the microwaves, thus cooking those areas by heat transference.

Food will cook more evenly in the microwave oven, if the food is arranged in a circle with the middle of the dish left empty (e.g., a tube pan) or if it is stirred frequently.

Food will not usually brown in a microwave oven. If a browned surface is desired, stick the cooked product under an oven broiler for a few minutes. Some foods, often high in fat or sugar, like chocolate or nuts, will burn in the microwave if overcooked.


In this unit you will learn the special food characteristics and techniques as they apply to microwave cooking.

Answer 3

the radiation waves excite water molecules in the food and the increased movement produces heat.