Microwave oven

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.To verify his finding, Spencer created a high density electromagnetic field by feeding microwave power into a metal box from which it had no way to escape. When food was placed in the box with the microwave energy, the temperature of the food rose rapidly.

Basic microwave ovens heat food quickly and efficiently, but do not brown or bake food in the way conventional ovens do. This makes them unsuitable for cooking certain foods, or to achieve certain effects. Additional kinds of heat sources can be added to microwave packaging, or into combination microwave ovens, to add these additional effects
In the 1960s, Litton bought Studebaker's Franklin Manufacturing assets, which had been manufacturing magnetrons and building and selling microwave ovens similar to the Radarange. Litton then developed a new configuration of the microwave, the short, wide shape that is now common. The magnetron feed was also unique. This resulted in an oven that could survive a no-load condition indefinitely. The new oven was shown at a trade show in Chicago, and helped begin a rapid growth of the market for home microwave ovens. Sales volume of 40,000 units for the US industry in 1970 grew to one million by 1975. Market penetration in Japan, which had learned to build less expensive units by re-engineering a cheaper magnetron, was faster.

Microwave ovens are generally used for time efficiency in both industrial applications such as restaurants and at home, rather than for cooking quality, although some modern recipes using microwave ovens rival recipes using traditional ovens and stoves. Professional chefs generally find microwave ovens to be of limited usefulness because browning, caramelization, and other flavour-enhancing reactions cannot occur due to the temperature range.On the other hand, people who want fast cooking times can use microwave ovens to prepare food or to reheat stored food (including commercially available pre-cooked frozen dishes) in only a few minutes. Microwave ovens are also useful for the ease in which they can perform some traditionally cumbersome kitchen tasks, such as softening butter or melting chocolate. Popcorn is one example of a very popular item with microwave oven users.

A consideration for rating the efficiency of a microwave oven is to assess how much energy is wasted by using other forms of cooking. For example, when heating water for a coffee, a microwave oven heats just the mugful of water itself. When using a kettle, an element heats the kettle itself plus the water plus any extra water which is then left unused in the kettle. Depending upon the size of the kettle and the amount of excess water, the efficiency of microwave ovens can be quite comparable. Cooking in conventional ovens entails heating the internal structure of the oven to cooking temperature and, additionally, it involves maintaining that temperature against convective and radiative losses of heat for a longer time than is usual with a microwave oven. The efficiencies of conventional cooking methods can be difficult to quantify but tend to be lower.


Food and cookware taken out of a microwave oven is rarely much hotter than 100 °C (212 °F). Cookware used in a microwave oven is often much cooler than the food because the cookware is transparent to microwaves; the microwaves heat the food directly and the cookware is indirectly heated by the food. Food and cookware from a conventional oven, on the other hand, are the same temperature as the rest of the oven; a typical cooking temperature is 180 °C (360 °F). That means that conventional stoves and ovens can cause more serious burns.

Due to this phenomenon, microwave ovens set at too-high power levels may even start to cook the edges of the frozen food, while the inside of the food remains frozen. Another case of uneven heating can be observed in baked goods containing berries. In these items, the berries absorb more energy than the drier surrounding bread and also cannot dissipate the heat due to the low thermal conductivity of the bread. The result is frequently the overheating of the berries relative to the rest of the food. The low power levels which mark the "defrost" oven setting are designed to allow time for heat to be conducted from areas which absorb heat more readily to those which heat more slowly. More even heating will take place by placing food off-centre on the turntable tray instead of exactly in the centre.