Microwave is a type of electromagnetic wave with an extremely short wavelength, ranging from 1mm to 1m, and its corresponding frequency is between 300GHz and 300MHz. To prevent microwave interference with radio communication, broadcasting and radar, the international community stipulates that there are four frequency bands used for microwave heating and microwave drying, namely: Band L, with a frequency of 890 to 940MHz and a central wavelength of 0.330m; The S segment has a frequency of 2400 to 2500MHz and a central wavelength of 0.122m. Section C, with a frequency of 5725 to 5875MHz and a central wavelength of 0.052m; The K band has a frequency of 22,000 to 22,250 MHZ and a central wavelength of 0.008m. Only the L and S segments are used in household microwave ovens. Microwaves are obtained by passing direct current or 50Hz alternating current through vacuum devices or semiconductor devices and utilizing the special movement of electrons in a magnetic field. This kind of motion can be simply explained as follows: From the perspective of electrical structure, there are two types of molecules in a medium: one is called electropolar molecular dielectrics, and the other is called polar molecular dielectrics. Under normal circumstances, they are all arranged randomly. If they are placed in an alternating electric field, the orientation of the polar molecules of these media will also change along with the polarity of the electric field. This is called polarization. The stronger the applied electric field is, the stronger the polarization effect will be. The faster the polarity of the applied electric field changes, the faster the polarization will be, and the more intense the thermal motion of the molecules and the frictional action between adjacent molecules will be. During this process, the conversion of electromagnetic energy to thermal energy is completed. When the heated substance is placed in the microwave field, its polar molecules swing and rub back and forth at a high frequency of several billion times per second with the microwave frequency, generating sufficient heat to heat food thoroughly in a very short time. Magnetrons are used in household microwave ovens to convert electrical energy into microwave energy. There are two types of magnetrons: pulse magnetrons and continuous magnetrons. Continuous wave magnetrons are used in microwave ovens. The propagation speed of microwaves is close to the speed of light. During its propagation, it can undergo reflection and refraction. It has three important characteristics related to heating. When microwaves encounter metallic objects such as silver, copper and aluminum, they are reflected just like visible light in a mirror. Therefore, metals are commonly used to isolate microwaves. In microwave ovens, metal is commonly used to make the box body and waveguide, and metal mesh with tempered glass is added to make the observation window of the oven door. When microwaves encounter insulating materials such as glass, plastic, ceramics, mica, etc., they will pass through as smoothly as light does through glass. Therefore, insulating materials are often used to make plates and pans without affecting the heating effect. When microwaves encounter food containing water or fat, they can be absorbed in large quantities and converted into heat energy. The microwave oven takes advantage of this feature to heat food.
Is microwave-processed food good? Is there any scientific basis for this?
Microwaves are high-frequency waves that change at a speed of 2.4 billion times per second, causing high-speed rotational motion of water molecules. They rub against each other, generating tremendous heat, which makes it convenient to cook food.
The pathogen contains a large number of water molecules. Under the action of microwaves in a microwave oven, all the bacteria can be killed within one or two minutes. It has been determined that when red intestines containing 1.92 million Escherichia coli per gram were heated in a 500-watt microwave oven, only 260 survived per gram after half a minute, and all were killed after one minute.
When cooking food in a microwave oven, since the heat is inside the food, it heats evenly and does not require stir-frying, thus avoiding the phenomenon of being burnt on the outside but burnt on the inside.
Nitrosamines are produced during the processing of foods such as cured meat, preserved meat, salted fish and smoked duck. Nitrite, as a preservative, can also react chemically with food to form nitrosamines, which can cause cell canceration. American pharmacologists have found that when cured meat is baked in a microwave for 45 minutes and taken out, it is both fragrant and crispy, with a delicious taste. Moreover, no trace of chalcosamine can be found through chemical analysis.
In addition, cooking meat products in a microwave oven can also fully protect the nutritional components of the meat products.
Mysterious stainless steel furnace cavity
A stainless steel microwave oven refers to a microwave oven with a cavity made of stainless steel. Stainless steel is an alloy steel made by adding a certain proportion of special elements such as nickel and chromium and through a special process. It has high corrosion resistance.
There are many types of stainless steel due to their different compositions and smelting processes. Among them, austenitic stainless steel is not easily magnetized due to the special internal molecular structure. On the surface, it seems that this kind of stainless steel cannot "attract" a magnet. Therefore, it is incorrect for users to use a "magnet" to test whether it is stainless steel. The microwave oven cavity made of stainless steel has the most prominent features of high surface strength, higher temperature resistance and rust resistance, etc.
The ordinary steel plate furnace cavity that has undergone surface coating treatment may have its surface coating layer fall off or crack after accidental bumps, thus losing its anti-rust effect on the ordinary steel plate. Compared with the ordinary steel plate furnace cavity that has undergone surface coating treatment, the stainless steel furnace cavity ensures that it is not prone to rust from the perspective of steel plate material. Even if there are large dents from bumps, it will not lose its "rust-free" characteristic.
It is a consensus that stainless steel is not prone to rust. For stainless steel microwave ovens in general household environments and usage conditions, it can also be considered that the stainless steel oven cavity will never rust. However, the ordinary steel plate furnace cavity that has undergone surface coating treatment may also experience rusting after long-term use, especially in the corner areas of the furnace cavity where rusting is more likely to occur.
Of course, this does not mean that the ordinary steel plate oven cavity treated with surface coating is extremely prone to rust. Judging from the current material, technological level, manufacturing cost and market acceptance, the ordinary steel plate microwave oven is not at a disadvantage, and there is no trend of being phased out due to the introduction of stainless steel microwave ovens.
As for some media's evaluation that stainless steel microwave ovens have higher heating effects and are more energy-efficient and time-saving, it is somewhat too one-sided. Compared with ordinary steel plates that have undergone surface coating treatment, the surface resistance of stainless steel materials is smaller. Under the action of microwaves, the surface eddy currents of this material are also smaller, which is manifested as low microwave loss and high reflectivity of this material. However, under the conditions of general household use, this difference is not easily noticeable.