How microwave cooking works

The microwave oven is one of the great inventions of the 20th century - millions of homes in the world have one. Just think about how many times you use a microwave every day:

Microwave ovens are popular because they cook food in an amazingly short amount of time. They are also extremely efficient in their use of electricity because a microwave oven heats only the food - and nothing else. In this article, we'll discuss the mystery behind the magic of "meals in a minute" with microwave cooking.

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 they are converted directly into atomic motion - heat. Microwaves in this frequency range have another interesting property: they are not absorbed by most plastics, glass or ceramics. Metal reflects microwaves, which is why metal pans do not work well in a microwave oven.

Microwave Cooking

You often hear that microwave ovens cook food "From the inside out." What does that mean? Here's an explanation to help make sense of microwave cooking.

Let's say you want to bake a cake in a conventional oven. Normally you would bake a cake at 180 C or so, but let's say you accidentally set the oven at 310 C instead of 180 C. What is going to happen is that the outside of the cake will burn before the inside even gets warm. In a conventional oven, the heat has to migrate from the outside of the food toward the middle. You also have dry, hot air on the outside of the food evaporating moisture. So the outside can be crispy and brown (for example, bread forms a crust) while the inside is moist.

In microwave cooking, the radio waves penetrate the food and excite water and fat molecules pretty much evenly throughout the food. No heat has to migrate toward the interior by conduction. There is heat everywhere all at once because the molecules are all excited together. There are limits, of course. Radio waves penetrate unevenly in thick pieces of food (they don't make it all the way to the middle), and there are also "hot spots" caused by wave interference, but you get the idea. The whole heating process is different because you are "exciting atoms" rather than "conducting heat."

In a microwave oven, the air in the oven is at room temperture, so there is no way to form a crust. That is why microwavable pastries sometimes come with a little sleeve made out of foil and cardboard. You put the food in the sleeve and then microwave it. The sleeve reacts to microwave energy by becoming very hot. This exterior heat lets the crust become crispy as it would in a conventional oven.

FACT BOX

How microwave cooking works - student2.ru

Cooking food with microwaves was discovered accidentally in the 1940s. Percy Spencer, a self-taught engineer, was building magnetrons for radar sets with the company Raytheon. He was working on an active radar set when he noticed that a peanut chocolate bar he had in his pocket started to melt. The radar had melted his chocolate bar with microwaves. The first food to be deliberately cooked with Spencer's microwave was popcorn, and the second was an egg, which exploded in the face of one of the experimenters. When food was placed in the box with the microwave energy, the temperature of the food rose rapidly. In 1945 Raytheon filed a U.S. patent for Spencer's microwave cooking process and an oven that heated food using microwave energy was placed in a Boston restaurant for testing. In 1947, the company built the Radarange, the first microwave oven in the world. It was almost 1.8 m tall, weighed 340 kg and cost about $5000 each. It consumed 3 kilowatts, about three times as much as today's microwave ovens, and was water-cooled. An early commercial model introduced in 1954 consumed 1600 watts and sold for $2,000 to $3,000. Raytheon licensed its technology to the Tappan Stove company in 1952. They tried to market a large, 220 volt, wall unit as a home microwave oven in 1955 for a price of $1,295, but it did not sell well. In 1965 the first popular home model was introduced at a price of $495. Sales volume of 40,000 units for the US industry in 1970 grew to one million by 1975. By the late 1970s the technology had improved to the point where prices were falling rapidly. Often called "electronic ovens" in the 1960s, the name "microwave ovens" later became standardized, often now referred to informally as simply "microwaves." Formerly found only in large industrial applications, microwave ovens were increasingly becoming a standard fixture of most kitchens. The rapidly falling price of microprocessors also helped by adding electronic controls to make the ovens easier to use. By 1986, roughly 25% of households in the U.S. owned a microwave, up from only about 1% in 1971. Current estimates hold that over 90% of American households have a microwave.

ANSWER THE QUESTIONS S

1. Why are microwave ovens so popular?

2. What is the commonly used radio wave frequency in the case of microwave ovens?

3. What interesting property do microwaves in this frequency range have?

4. How microwave cooking works - student2.ru What does it mean to cook "from the inside out"?