It should be noted that microwave ovens can only cook, not bake. Don't talk about roast duck, not even baked sweet potatoes and steamed bread. When steamed bread is heated, the skin is soft, often the skin is not pasted, and the steamed bread core is pasted first.
Why? Because we have learned in heat, there are three ways of heat transfer: conduction, convection and radiation. Boiling water depends on heat conduction and convection. Steamed steamed bread is heat conduction and convection. Cooking is mainly heat conduction, while baking steamed bread is heat radiation. Thermal radiation is mainly transmitted by infrared radiation. In the sun, we feel that the sun hurts our skin, and we feel that the panic of baking is caused by the infrared radiation of the sun. Thermal radiation is characterized by direct propagation, without any medium, and from outside to inside. When baking sweet potatoes, it is hot outside and hot inside; The skin is burnt and the inside is cooked.
This is obviously not the case in the microwave oven. There is no heat energy, no heat transfer and no infrared ray in the microwave oven. It relies on a high-frequency electromagnetic wave, that is, microwave as a medium to transmit energy. The wavelength of microwave is 1mm to 1m (frequency is 300 MHz to 300 GHz). A microwave oven is actually an oscillator that generates microwaves. The wavelength of the microwave it generates is 122 mm and the frequency is 2450 MHz.
Microwave oscillates in the microwave oven, making the water molecules contained in food oscillate at the same frequency. Causing molecules to rub against each other. Friction generates heat. The higher the oscillation frequency, the greater the amplitude, the more intense the intermolecular friction and the more heat generated. Obviously, the effect of this heating method is different from that of baking infrared radiation. It can heat both the inner and outer surfaces of food. This heating method is very efficient. It only takes a few minutes to cook a box of rice, but you will never get the effect of "the outside is burnt and the inside is tender" Toast, kebabs and sweet potatoes can only be used in electric ovens. Some students may have noticed that microwave ovens are not only "soft on the outside, but also" tender in Jiao Wai ". If you heat the steamed bread for a little longer, the core of the steamed bread will become hard and thin. Why is this? The main reason is that the microwave emitted by the microwave magnetron is not evenly distributed in the microwave oven, but "focused" in a certain position in the oven, which means that the microwave intensity here is hundreds of times higher than that in other parts. This gathering position is about a few centimeters above the center of the turntable, showing a mushroom-like position. If you heat a big steamed bread here, you will find that the surface of the steamed bread is not hot yet, but the heart of the steamed bread has dried up and formed a mushroom-like core. To avoid uneven heating of food, there is a turntable in the microwave oven. After opening, it will automatically keep rotating, so that the food can be heated evenly.
The food containers used in microwave ovens are very picky. Usually, ceramics or special plastics can be used. Not metal or enamel. This is because microwave will "short circuit" and reflect when it contacts metal products. If food is heated in a metal container, the temperature of the food in the container will not rise even if it is burned for an hour. This is because the microwave will reflect back immediately after it meets the metal container, and the food will not be heated by the heat source. What is more dangerous is yet to come, because all high-frequency microwaves are reflected back, which will form a "high-frequency short circuit" in electronic technology, resulting in the anode temperature of the electron tube emitting microwaves being too high and burning red.
Some people say that microwaves are harmful to people's health, so is it dangerous to use microwave ovens? It should be said that microwave is definitely harmful to human body. The key point is that people take this into account when designing microwave ovens to prevent microwave exposure and make them very safe. Its metal shell and glass window can block the microwave. When the oven door is not tight, the microwave oven will stop working immediately, so the microwave oven is very safe.
The microwave power generated by microwave oven is relatively high, generally ranging from 600 watts to 2000 watts, and food molecules vibrate 2.45 billion times per second in high-frequency microwave. Therefore, the heated food is cooked in a short time. The microwave oven itself does not have the process of heating the furnace or air, but directly converts electromagnetic energy into heat energy of food, so it has high efficiency and low energy consumption.
Matters needing attention
1, avoid using ordinary plastic containers: use special microwave utensils to hold food and heat it in the microwave oven. First of all, hot food will deform plastic containers. Second, ordinary plastics will release toxic substances, pollute food and endanger human health.
2. Avoid using metal utensils: Because there are utensils such as iron, aluminum, stainless steel and enamel in the furnace, electric sparks will be generated when the microwave oven is heated, which will not only damage the furnace body, but also heat the uncooked food.
3. Avoid using closed containers: use wide-mouth containers when heating liquids, because the heat generated by food heating in closed containers is not easy to dissipate, which makes the pressure in the containers too high and easily leads to blasting accidents. Even if you use shells to cook food, you should pierce the shells with needles or chopsticks in advance to avoid bursting after heating, splashing out to pollute the furnace wall or injuring people.
4. Avoid overtime heating: food is thawed or heated in the microwave oven. If you forget to take it out, if it takes more than 2 hours, you should throw it away to avoid food poisoning.
5. Don't heat the meat until it is half cooked, and then put it in the microwave oven: because bacteria will still grow in the half cooked food, put it in the microwave oven for the second time, because the time is too short to kill all the bacteria. Frozen meat must be thawed in the microwave oven before it is heated and cooked.
6. Avoid freezing the meat thawed in the microwave oven again: Because the outer layer of the meat has actually been heated at a low temperature after thawing in the microwave oven, bacteria can reproduce at this temperature. Although freezing can prevent its reproduction, it can't kill the living bacteria. If the meat thawed in the microwave oven is frozen in the refrigerator again, it must be heated until it is fully cooked.
7, avoid fried food: because high-temperature oil will splash and cause fire. In case of accidental fire in the furnace, don't open the door, turn off the power first, and then open the door to cool down after the fire is extinguished.
8. Avoid putting the oven in the bedroom: At the same time, be careful not to cover the cooling window grille on the microwave oven with objects.
9. Avoid working in front of the microwave oven for a long time: After turning on the microwave oven, people should stay away from the microwave oven or at least 1 m away from the microwave oven.
The use and maintenance of microwave ovens should pay attention to the following points:
(1) The microwave oven should be placed in a ventilated place, and there should be no magnetic substances nearby, so as not to interfere with the uniform state of the magnetic field in the furnace cavity and reduce the working efficiency. Keep a certain distance from TV and radio, otherwise it will affect the visual and auditory effects.
[2] When cooking food, don't put it in the oven and don't work with electricity. Don't let the microwave oven run with no load, or it will damage the magnetron. In order to prevent careless no-load operation, a glass filled with water can be built in the furnace cavity.
[3] All heat-resistant containers such as metal tableware, bamboo, plastic and lacquerware, and concave-convex glass products are not suitable for use in microwave ovens. Porcelain dishes can't be inlaid with honeysuckle. Containers for food must be placed in special plates for microwave ovens, not directly in the oven cavity.
[4] The heating time of microwave oven depends on the material and dosage, and it is also related to the freshness and water content of food. Because the heating time of various foods is different, it should be shorter when the heating time required for food is uncertain, and the heating time can be increased according to the raw and cooked degree of food after heating. Otherwise, if the time is too long, the food will harden and lose its fragrance, color and taste. Adjust the timing and power (temperature) knob according to the food type and cooking requirements, so that you can read the instructions carefully and understand them.
[5] Eggs with shells and sealed food cannot be cooked directly. In case of explosion.
[6] Ensure that the oven door is closed, and ensure that the interlock switch and safety switch are closed. After the microwave oven is turned off, it is not appropriate to take out the food immediately, so there is still residual heat in the oven and the food can continue to cook. /kloc-it's better to take it out after 0/minute.
[7] The stove should always be kept clean. After disconnecting the power supply, wipe it with a damp cloth and neutral detergent. Do not rinse or let water flow into the electric appliances in the furnace.
(eight) regularly check around the oven door and door lock. In case of damage or poor sealing, stop the machine to prevent microwave leakage. It is not advisable to put your face near the observation window of the microwave oven, so as not to hurt your eyes by microwave radiation. It is also inappropriate to be exposed to microwaves for a long time, so as not to cause dizziness, dizziness, fatigue, emaciation, hair loss and other symptoms, which will cause damage to the human body.