MICROMANAGING YOUR MICROWAVE

By Alma Copeland, Home Economist

TEAM Resources

How does a microwave cook?

Essentially microwaves steam foods. The waves pass through china, glass and paper without affecting them; they work by causing the water molecules in food to vibrate and produce heat.

Do microwaves cook food from the inside out?

No. The waves cook the outside first, and then heat is conducted to the interior. The interior can get much hotter than the outside layer if there is a lot of water in the middle. It pays to be cautious when taking a first bite of microwaved food.

Why do gold-rimmed plates cause a spark?

Microwaves are an electromagnetic field, which is why you shouldn't cook in metal containers. Very thin metals such as the wire in a twist-tie, a gold rim or a bit of foil can't absorb the current and are especially likely to heat up and spark. Some metals, like the rim of a frozen juice can, won't spark. Some metals are okay in combination microwave/convection ovens.

How can you tell if a dish is microwave-safe?

Put the empty dish in the microwave along with a cup of water in a glass container. Microwave on high for one minute. If the dish gets hot, don't use it. If it stay cool, it's safe to use.

Is all paper safe?

No. Some paper is a fire hazard. You can use wax paper, cooking bags, parchment paper, paper plates and white paper towels. Don't use recycled paper, newsprint or brown grocery bags. Recycled material may have minute amounts of metal that can cause a fire. White is usually safer than printed or tinted paper.

Is it safe to use plastic wrap and other plastics in a microwave?

Many are safe. People have been told to be aware of dangerous chemicals called plasticizers that leach into foods in the microwave. No one knows if these chemicals are a danger, especially in the small amounts that might contaminate foods in a microwave. All plastic wraps on the market are deemed safe, but polyethylene wraps such as Saran or Glad Cling Wrap can be used if you want to be sure of avoiding plasticizers. To be on the safe side, don't let the plastic wrap touch the food while heating. When meat or other foods come tightly wrapped in plastic, remove the wrap before microwaving. Don't put margarine tubs or plastic bags in the microwave, since they may warp, melt and/or burn you. Avoid reusing the trays and cartons prepared foods come in; they are meant to be thrown away after one use.

What foods are likely to explode in a microwave?

Anything in a tight skin or shell as the water inside can expand and burst out. Before microwaving a potato, prick the skin or remove a strip of peel. Always halve winter squash and similar vegetables before microwaving. Don't put an egg in the microwave without removing the shell. Microwaving is fine for scrambled or poached eggs (pierce the yolk so it won't burst).

How long have microwave ovens been around?

The microwave oven came out of World War II technology. About l946 a scientist at Raytheon in the U.K. was working on a radar vacuum tube called a magnetron. He discovered that microwaves produced by the magnetron had melted the chocolate bar in his pocket. By the late l970s microwave ovens were in wide use.

Are microwaves like X-rays?

Microwaves are a form of electromagnetic radiation, like light and electricity. There are no X-rays in a microwave oven.

Do the ovens leak radiation? In Canada, the United States and many other countries, microwave ovens must meet safety standard that lasts throughout the lifetime of the appliance. They must have an interlock system that shuts down microwaves as soon as the door latch is released. If the first system doesn't operate; there is a second device that shuts it down. Ovens are highly resistant to leakage. Still, if you have a very old microwave (30 years old or more), consider buying a new one. Don't let anybody sell you a "microwave tester". If you want the oven tested, take it to a service shop.

Does microwaving leave dangerous compounds in foods?

No, in spite of Internet sites that claim otherwise. Microwaving is simply heating and is as safe as conventional cooking. It doesn't do anything to food molecules that a regular stove doesn't do. It does not alter DNA or create free radicals. One of the strongest rumors is that you must not eat microwave foods while undergoing radiation therapy. This is not true.

Is it okay to warm a baby bottle in the microwave?

Yes, but when microwaving any food or liquid for a child, be certain it isn't hot enough to burn. Stir or shake it to eliminate hot spots. Test it in advance. The bottle might be cool, but the formula could still be too hot to drink.

If you have a pacemaker, should you avoid microwaves?

No. Older microwaves that leaked may have interfered with pacemakers, and you used to see hazard warning about this. The current models have minimal leakage. Furthermore, pacemakers now have a shield against electromagnetic waves. There is no reason to worry.

Does micowaving destroy nutrients?

All cooking destroys some nutrients, but because microwaving is fast and uses less water, you end up with more nutrients than with other methods. Use only two or three tablespoons (30 to 45 mL) of water when microwaving veggies.

What is the worst problem with microwaving? Probably that it tends to cook unevenly, leaving undercooked spots - a potential cause of food poisoning. A turntable (featured in many models) can help, or you can turn the food yourself halfway through the cooking period, or stir it. When cooking meat, check with a meat thermometer in several places to make sure it is done. Meat with bones may be more difficult to cook evenly.

Source: University of California, Berkeley, Wellness Letter, September 2005.