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# Why is it that breads heated with a microwave cool much faster than those heated with an oven?

###### Wiki User

The heat from a oven is slowly passed into the bread and the substance holds the heat upon removal relative to the time of heating. For a microwave, the substance is artificially raised in temperature from the outside in. As soon as the heat is stopped, the temporary warming stops and the core of the object is not as warm as the outer layers, pulling the heat inward. Cool replaces the heat as it goes inward. http://www.gallawa.com/microtech/howcook.html All liquids and food products, are made up of molecules. These molecules have positive and negative particles, so they tend to behave like microscopic magnets. As the positive half cycle of the microwave penetrates the food, the negative particles of the molecules are attracted and attempt to align themselves with this positive field of energy. Then, when the microwave energy alternates to the negative half cycle, the opposite occurs -- The negative particles are repelled and the positive particles are attracted, causing a flipping motion (actually, this reaction is the movement of the particles within each molecule, so, technically, they reverse polarity). This might be compared to a room full of people trying to run back and forth, from one side to the other. Obviously, there would be a lot of bumping, rubbing, agitation, and friction. Now, consider that the actual frequency of the RF energy used in microwave ovens is 2450 million cycles per second! Moreover, consider that within the course of one of those cycles, the molecules would actually change their direction (polarity) twice - once for the positive half-cycle and once for the negative half-cycle. This red-hot rate of vibration causes tremendous friction within the food, and - just as rubbing your hands together makes them warm - this friction produces heat. So the heat is produced directly in the food, but the food is not cooked, as is commonly believed, from the inside out. Actually, the cooking begins just beneath the outer surface and from there inward and outward, with the majority of the energy being expended in the outer layers. The rate and degree of heating depend on the depth and density of the food, as well as its ability to conduct heat. Because the microwave energy is changed to heat as soon as it is absorbed by the food, it cannot make the food radioactive or contaminated. When the microwave energy is turned off and the food is removed from the oven, there is no residual radiation remaining in the food. In this regard, a microwave oven is much like and electric light that stops glowing when it is turned off.

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