Principles of microwaving

Microwaves, such as those used in cooking and processing food, are part of the broad spectrum of electromagnetic radiation. Electromagnetic waves are waves of electrical and magnetic energy moving together through space. They include gamma rays, x-rays, ultraviolet radiation, visible light, infrared radiation, microwaves and the less energetic radio waves.

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 the alternating electromagnetic field generated inside the microwave oven would lead to excitation, rotation/collision of polar molecules and ions inside the food. These molecular frictions would generate heat and subsequently lead to temperature rise.

Microwaves in this frequency range have another interesting property: they are not absorbed by most plastics, glass or ceramics.

The propagation mode of microwave and light is very similar, so microwave has a strong light transfer characteristic. They are all spread in a straight line. And when the microwave encountered an object which has a large size of its wavelength, it will be reflected. And metal reflects microwaves, which is why metals cause spark in a microwave oven.

In microwave cooking, the radio waves penetrate the food and excite water and fat molecules pretty much evenly throughout the food. There is no “heat having to migrate toward the interior by conduction”. There is heat everywhere all at once because the molecules are all excited together.
Principles of microwaving

Microwave oven technology

The microwave oven is an electronically controlled home appliance used for cooking. It uses the principle of dielectric heating at microwave frequencies. The frequency of microwaves is 2459 MHz.

Microwave heating has several industrial applications such as product drying and large-scale heating and processing, but the main application is in household and commercial cooking.

A microwave oven works because the microwaves pass through the food container and into the food. They can pass easily though most kinds of plastic, paper, glass and any pottery or china without metal trim, paint or glaze.

The microwaves are generated in the cooking cavity. These microwaves are reflected from the walls of the cavity and strike the food. Because of these high frequency waves the heat is induced inside the food. The temperature increases much faster than the conventional cooking.

The heat is conducted inside the food and it is cooked in short time. Although microwaves will generally not damage cooking utensils, it is important to remember that the heat of the food may sometimes do so. For example: syrup heated in a glass utensils would reach such a high temperature that the glass would break.
Microwave oven technology

Microwaving the food

The absorption of microwave by a dielectric material results in the microwaves giving up their energy to the materials with a consequential rise in temperature. Food composition (mainly water content) is a key factor that determines how fast it will heat in a microwave environment.

Cooking food using a microwave oven is accomplished by setting an appropriate amount of time necessary for the waves to penetrate the food and cook it.

The most important advantages of microwave heating is that microwaves are capable of penetrating very deeply into certain materials heating extend within the entire food material, which result in very significant reductions in process heating times for drying, thawing, sterilization and so on.

There are limits to the depth of their penetration. The geometry of the food to be heated is an important consideration; conduction and convection may often take far longer to heat a given mass of food.

Microwaves generate heat due to their interactions with the food materials. The microwave radiation itself is non-ionizing radiation, distinctly different from ionizing radiation such as X-rays and gamma rays.

Heating foods evenly in a microwave oven is difficult at best, particularly with solid foods of different composition.

A major use of microwaves in the food industry is the tempering and thawing of frozen foods, especially meat, fish, butter and fruit.
Microwaving the food