THEORY OF MICROWAVE COOKING
Cooking with microwaves has transformed modern food preparation technology. With the introduction of the microwave oven in the mid 1970s, food preparation has become more efficient and convenient. It generally takes less time to cook food by microwaves than by conventional methods, and microwave ovens consume much less energy.
MICROWAVE COOKING
Microwave cooking is accomplished by penetrating food with high frequency electromagnetic waves, called microwaves. Microwaves have the unique characteristic of:
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Reflecting off metals.
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Passing through most glass, paper and plastics.
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Being absorbed by foods containing fats and liquids.
THEORY OF MICROWAVE COOKING
Cooking with microwaves has transformed modern food preparation technology. With the introduction of the microwave oven in the mid 1970s, food preparation has become more efficient and convenient. It generally takes less time to cook food by microwaves than by conventional methods, and microwave ovens consume much less energy.
MICROWAVE COOKING
Microwave cooking is accomplished by penetrating food with high frequency electromagnetic waves, called microwaves. Microwaves have the unique characteristic of:
-
Reflecting off metals.
-
Passing through most glass, paper and plastics.
-
Being absorbed by foods containing fats and liquids.
In conventional ovens, first an element is heated. Then the surrounding air is heated, followed by the walls, the racks and the pan. Finally the surface of the food is heated, and this heat is conducted from the surface to the interior to cook the food.
Microwave cooking differs from conventional cooking in that heat is produced instantly in food as it absorbs microwave energy. Cooking heat is produced in the food rather than externally.
In microwave cooking, the greater penetration of the microwaves will instantly affect molecules in and below the surface of the food. These molecules are stimulated by the microwaves much the same as magnets are affected by an electromagnetic field. The molecules oscillate with the microwaves as they penetrate the food.
Microwaves oscillate, or change polarity from positive to negative, at 4900 million times-per- second. Since water and fat molecules within food contain positive and negative charges, exposing the food molecules to a microwave field causes the molecules to align themselves with the microwave energy. Each time the microwave energy changes polarity, the molecules again try to align themselves with the field. Thus, by oscillating the molecules 4900 million times-per-second, (2450 Megahertz), tremendous friction is created producing the intense heat necessary for rapid cooking.
All of the heat is produced inside the first 3/4" to 2" of the foods surface.
If the food is thicker than 2", the heat will continue to conduct itself through the food to complete the cooking process. Some microwave cooking instructions say that the food should “stand” for a period of time after being removed from the oven so the internally-produced heat has time to be conducted throughout the food.
ELECTROMAGNETIC ENERGY AND MICROWAVES
Microwaves are ultra-high-frequency electromagnetic waves, not heat waves. An electromag- netic wave is energy that travels at the speed of light in organized and measurable waves, or cycles, and creates electromagnetic fields.
Depending on the frequency of the wave, the energy that is produced can be used in a number of applications. Radio and television signals are electromagnetic waves. Visible light, as well as infrared and ultra-violet light are also electromagnetic waves. In addition to cooking, microwaves are also used to transmit data, voice, radio, and television across long distances on land or to and from satellites orbiting the earth.
Electromagnetic waves are classified in an electromagnetic spectrum according to wavelength and frequency. In the United States the use of the electromagnetic spectrum is regulated by the Federal Communications Commission. The following chart shows the classification of electromag- netic waves.
Browning of meats and other foods is not as noticeable as with conventional cooking, although roasts, turkeys and other bulkier meats requiring a longer cooking time brown just as in conven– tional cooking.
Now that we know how food cooks in a microwave oven, what is a microwave? What does a microwave look like? If we could see a microwave, it is about 4.8 inches long, and about the thickness of a pencil.
4.8"
By the formula C (Speed of Light) / F (Frequency) = W (Wavelength) we can determine the wavelength of cooking microwaves at approximately 12 cm or 4.8 inches.
300,000 Km/sec. (Speed of Light) 2,450 MHz (Frequency)
= 12.2 cm (Wavelength)
The ultra high frequency of 2,450 MHz has been assigned to microwave ovens. MHz or Mega Hertz means a million cycles per second.
One characteristic of microwaves is important to note here. The only effect microwaves have on fat and water is to cause the molecules to move rapidly. Microwaves do not cause any changes to the molecule’s structure, or its genetic contents.
Forms of wave energy with frequencies up through visible light, are called nonionizing energy. Nonionizing energy does not change cellular, or genetic structure, and does not accumulate in tissue after repeated exposure. Microwaves are within this group of electromagnetic waves, and are said to be “nonionizing.”
By contrast, energy waves with extremely high frequencies and short wavelengths, are considered ionizing energy. Exposure to ionizing energy, such as X-rays, gamma, or cosmic rays, can be damaging to living tissue, because these types of wave energy can change cellular and genetic structure. Ionizing energy also builds-up, or accumulates, after repeated exposure.
X-Rays Gamma Rays Cosmic Rays
The effects of wave energy are dependent on the wavelength and relative strength, or amplitude, of the wave. Electromagnetic waves that are relatively strong at the source lose their strength in inverse proportion to the square of the distance from the source. Television transmissions in the thousands of watts at the source are only detectable by extremely sensitive electronic circuits, and they have no effect on people. In a similar manner, the energy level measured just 16 inches away from a microwave oven, would drop to just 1/256 of the energy level measured inside (at the source).
Because of the relatively high frequency and high energy level of microwaves, and the short distance between the source of the microwaves and the food confined in a properly operating microwave oven, the energy waves remain strong enough to cause the water and fat molecules in food to oscillate, or move, to align themselves with the positive and negative cycles of the microwaves. This vibration causes friction between the molecules, which in turn, causes heat to build up.