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MICROWAVE OVEN. While experimenting with radar during World War II, Percy Spencer of Raytheon Corporation in Waltham, Massachusetts, discovered the heating properties of microwaves. With a candy bar in his pocket, he leaned in front of the microwave tube and the candy bar promptly melted. This event led to the birth of microwave ovens.

In 1945 Spencer submitted his first patent application for heating food with microwaves. The patent described two parallel magnetrons that heat food that passes by on a conveyor belt. Two years later, William M. Hall and Fritz A. Gross, Spencer's co-workers, applied for a patent for a microwave-heating device enclosed in an oven. This device consisted of two microwave-generating magnetron tubes packed in a metallic box. The oven included a timer and a means of controlling power.

Raytheon's president, Laurence Marshall, was interested in Spencer's patent. A prototype microwave oven was constructed in 1946 costing an estimated $100,000. Marshall was also enthusiastic about the prototype and ordered engineers to develop an oven in which cold sandwiches could be heated. A contest was held to name the new oven—the winner was "Radarange."

Commercial Microwaves

The first commercial Radarange model was a freestanding white-enamel unit operating at 220 volts of electricity and with an internal water-cooling system. The first Raytheon microwave oven was sold to a restaurant in Cleveland, Ohio, in 1947. Subsequent Radaranges incorporated sliding vertical doors. With a price tag of $3,000, sales were mainly limited to restaurants, railroads, cruise ships, and vending-machine companies.

Development of the microwave oven continued during the 1950s. Raytheon dominated the field of commercial microwave ovens and heating applications: It was the only manufacturer of ovens for restaurants and was the principal magnetron manufacturer. Raytheon licensed other companies, such as Hotpoint, Westinghouse, Kelvinator, Whirlpool, and Tappan, to manufacture the ovens. Raytheon furnished power supplies, magnetrons, and basic-oven design data to each company. The Tappan Company began experimenting with a Radarange installed in their lab. Tappan engineers, who were experts in cooking, teamed up with the Raytheon microwave engineers. In January 1952 the Tappan Company developed the first domestic commercial Radarange. It was powered by a 1,400-to 1,700-watt magnetron that was water cooled and required plumbing connections. The unit was five and a half feet high and weighed 750 pounds.

Domestic Microwaves

The experimental unit developed by Tappan was impractical for domestic use. What was needed was a magnetron requiring less power and a heat dislocation system that could replace the water cooling mechanism. Tappan engineers designed a cabinet with an air-cooled system. Eventually, the magnetron and related components, which had fed microwaves directly into the cavity, were relocated behind the oven. In October 1955, Tappan introduced the first domestic microwave oven for the consumer market. Designed to fit a standard forty-inch range or for built-in use, the unit had a stainless-steel exterior and aluminum oven cavity with a glass shelf. The oven featured two cooking speeds (500 or 800 watts), a browning element, timer, and a recipe-card file drawer. It retailed for $1,295. The unit was marketed as an "electric range." Its advertised advantages were cooking speed, a cool oven, and a unique reheating capability.

General Electric's Hotpoint division, which also had been researching microwave cooking, unveiled its electronic oven the following year. Both the Tappan and Hotpoint oven generated unprecedented enthusiasm and interest in 1956, but sales were dismal. The price was high for the average consumer, and food-processing techniques for the microwave were not well understood. Few food processors took the technology seriously, thus few microwaveable foods were produced.

Breakthroughs

Tappan continued to improve its product. By 1965 Tappan had introduced the first "microwave cooking center," which consisted of a microwave oven mounted above a conventional range. This unit still retailed for well over $1,000. Despite these advances, only ten thousand households in the United States owned microwaves by 1966.

Two events revolutionized the microwave industry. The first was the invention by Keisha Ogura of the New Japan Radio Company—40 percent of which was owned by Raytheon—of a compact, low-cost magnetron. The second was Raytheon's acquisition of Amana Refrigeration, Inc. George Forestner, Amana's president, was a microwave visionary. Amana appliance engineers teamed up with Raytheon experts to develop and design a household Radarange. In August 1967, Amana released its first microwave oven, the Amana RR-1. It operated at 115 volts and sold for $495. The unit was well received. The Amana RR-1 set off a revolution in microwave oven technology, and Amana's success encouraged other appliance manufacturers to produce microwave ovens.

Another important microwave oven manufacturer was Litton, which acquired a small microwave manufacturer called Heat & Eat in 1964. Previously, Litton had manufactured commercial microwave ovens for restaurants. Its newly named Microwave Cooking Products Division in Minneapolis targeted the home market. Litton's Model 500 used 115 volts and was compact. These ovens were installed on TWA planes in 1965, and Litton dominated the restaurant business by 1970.

Microwave Challenges

Despite the initial successes, there were still problems to overcome before the microwave oven would be generally accepted. Manufacturers needed to convince the public that microwave ovens were safe. This fear began with the U.S. Congress's passage of the Radiation Control for Health and Safety Act in 1968. On 4 January 1970, the U.S. Department of Health, Education, and Welfare published the results of microwave oven radiation tests. The tests showed that microwave ovens leaked microwaves. Thus the federal government developed new standards and required changes in the construction of ovens beginning on 6 October 1971. These new regulations required design changes that would result in safer microwave ovens. Public apprehension slowly abated.

Another crucial challenge was convincing food processors to repackage their products. Foods packed in foil blocked microwaves and damaged ovens. Also, frozen foods contained too much water for microwave use. At first, food processors were not interested in working with microwave manufacturers. By the 1970s, however, more than 10 percent of all U.S. homes possessed microwaves, many microwave ovens were in use in vending businesses, and numbers were steadily increasing. Major food processors quickly reversed their direction and invested in microwaveable food products, and specialized microwave cookware was introduced. By 1975 microwave ovens out-sold gas ranges, with sales of over one million units. In the early twenty-first century, the primary use of microwave ovens in the United States was to reheat food.

See also Fast Food; Frozen Food; Kitchen Gadgets; Kitchens, Restaurant; Popcorn; Preparation of Food; Storage of Food.

Andrew F. Smith