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MICROWAVE OVEN

By Janet Spencer

The microwave oven revolutionized cooking in the 20th century. Over 90% of American homes have at least one.

  • Many of today’s products and technology are the by products of discoveries during WWII and the microwave oven is one of them. In 1946, an engineer named Percy Spencer worked for the Raytheon Corporation in Massachusetts – the largest manufacture of the magnetron (a vacuum tube that produces microwave radiation), used to make radar systems operate.
  • America and it’s allies desperately needed stronger radar systems with a longer reach to detect the enemy from further away. Spen-cer’s assignment was to improve this technol-ogy.
  • On one particular day in the research lab, Spencer made a surprising discovery that would revolutionize cooking. While standing near a magnetron, he felt heat radiating from the tube and noticed the chocolate bar in his pocket had melted.
  • Wondering if in fact the high frequency radio waves emitting from the magnetron had heated up the chocolate, he placed a handful of popcorn kernels near the device to see what would happen. He watched in amaze-ment as the corn began to pop. After further experiments, he realized that microwaves cook foods, and fast. Much faster than con-ventional ovens that cook with heat.

The Raython company knew the war was coming to an end and needed to develop new products for the peace time economy. Upon learning what Spencer had discovered, Ray-thon CEO, Lawerence Marshall, put Spencer in charge of taking this military technology and turning it into a household appliance.

  • Spencer designed an enclosed metal box with an opening just small enough to supply mi-crowave energy to it. Food placed inside the box heated rapidly and cooked in no time at all. The idea of cooking with microwaves was patented by Raytheon in 1946.
  • By 1947, the first commercial microwave ov-en was manufactured. This large oven was housed in a refrigerator sized cabinet, stand-ing 5ft 11 in (1.8 meters) and weighing 750lbs (340 kilograms). It used a radar quali-ty magnetron putting out 3000 watts of pow-er. The design needed special plumbing to water cool the magnetron. The oven cooked so fast the company dubbed it “stop watch cooking.” A well done steak would cook in 50 seconds.
  • Wanting to manufacture a smaller, less pow-erful oven for the general public, Raytheon acquired the Amana company in 1965, and in 1967 they introduced the first popular home model, the countertop Radarange, with a price tag of US$495.
  • The technology used in a microwave oven to cook food is with the use of  high frequency radio waves (electromagnetic wave energy) trapped in a metal box, transmitted by a magnetron. The waves penetrate food, excit-ing water, fat and sugar molecules  causing them to vibrate at such a high velocity, the friction creates heat, which cooks the food.
  • When using electromagnetic waves to heat and cook food, certain precautions should be taken. Let’s look at a few safety measures when using a Microwave oven:
  • Because microwaves excite a foods molecules, not all these molecules heat at the same rate. This is how microwaved food can end up with hot and cold spots. In  poultry, meat and eggs the cold spots may not be taken above the temperature required to kill bacte-ria. One solution is covering  food with a vented lid. This method builds up hot steam under the lid, raising the temperature enough to kill any bacteria and helps cook food more evenly. A meat thermometer can also be used to ensure that food is cooked to the right temperature.
  • Microwaves can heat your body by adding thermal energy to the water molecules in you. This heating can be damaging if it’s not con-trolled. Most of your body is protected from slow heating because blood carries heat away from any local hot spots, but the cornea of the eye has no cooling blood flow making it prone to overheating when exposed to mi-crowave radiation so it’s important not to use a microwave if the door doesn’t shut proper-ly, or the protective screen in the glass is torn. The door keeps the energy inside, where it needs to stay!
  • If concerned about microwave leakage, there are microwave leakage meters available at most hardware stores. It is recommended to stand 20 inches (51 centimeters) or more from a microwave while in use, so if there is a radiation leak, this will minimize exposure. Keep children away while using a micro-wave.
  • Water is capable of being “supper heated” when it reaches temperatures above it’s nor-mal boiling point (100C or 212F), causing a boiling delay. When anything is put into the water it suddenly erupts – spitting water eve-rywhere which can result in sever burns.
  • Solid foods cooked in the microwave can build up pressure (in the form of steam), from the water molecules heating to a boil. When the steam escapes, it can causes food to pop and explode. This pressure can continue to escape even after the microwave turns off. It is advisable to let food stand in the micro-wave for one minute before removal to avoid burns.
  • Plastic containers should not be used in the microwave unless they are marked micro-wavable safe. Glass is preferable. Never use plastic wrap as a cover – it melts and contam-inates the food with plastic toxins.
  • Metal can produce dangerous arcing in a mi-crowave oven so don’t put metal objects, containers or cooking utensils in the micro-wave. Also don’t use cups or plates with metal decorations, recycled paper products (they may contain metal fragments), Styrofoam cups, aluminum foil, twist ties and ceramics with a lead based glaze.
  • Never operate a microwave without food or liquid inside. If your oven is empty and there is nothing to absorb the microwave energy, (glass and microwavable containers don’t ab-sorb microwaves) the energy can feed back to the microwave oven itself. This can perma-nently damage the magnetron.
  • A Microwave should be taken to a recycling center for disposal. Some of the metal can be reused. Depending on how old the micro-wave is, the magnetron may contain a small amount of beryllium oxide which is a known carcinogenic.