Microwave Ovens: To Zap or Not To Zap

To zap or not to zap

More than 90 million American kitchens have a microwave oven. You don’t need one to eat healthfully or have a green kitchen. But a microwave can shave off some of your energy use, especially if you cook smaller meals or use the kitchen mostly to reheat takeout or warm frozen foods.


Top Tips

At home

  • Zap small meals. If you have small to medium quantities of food, it’s much more energy efficient to cook in a microwave than in a conventional or convection oven or on the stovetop. The energy and time savings decreases with larger volumes of food, however. (Keep in mind that microwaves aren’t suitable for certain types of cooking, such as roasting, grilling, or baking.)
  • Don’t zap baby bottles. Don’t use a microwave to heat milk in a baby bottle. It┬ácan heat food unevenly, so there may be dangerous “hot spots” you may not detect when checking the bottle’s temperature. Plus some bottles contain a chemical known as BPA, which can be harmful to children, and is believed more likely to leach into products when used in the microwave.
  • Close the door securely. Like a conventional oven, a microwave uses radiation to heat food. But conventional cooking uses “infrared” radiation, or heat, and microwaves use a different part of the electromagnetic spectrum–“microwave radiation.” When exposed to microwave energy, water molecules in the food vibrate, converting the energy into the heat that cooks the food. While it’s true that human exposure to intense microwave radiation can cause harm, microwave ovens are designed to contain the microwaves within the oven. They do not produce energy if the door is open. If the oven is damaged, however, radiation leakage is possible. Never use a unit that is malfunctioning or has a damaged door, latch, or seals. Keep the door and seal free from food residue, so that the door closes securely. If you suspect a problem with the oven, stop using it and contact the manufacturer.
  • Don’t use┬áplastic. Packaging containers like margarine or salsa tubs should never be put in the microwave. The U.S. Food and Drug Administration says that plastic containers and plastic wrap labeled “microwave safe” are okay to use, but that the plastic wrap shouldn’t touch the food during microwaving. On the other hand, some experts advise against using any plastic containers or plastic wrap in the microwave because chemicals could potentially migrate from the plastic into hot food. Until there’s a definitive answer, the safest approach is to use a microwave-safe glass or ceramic container with a lid. If you don’t have a lid, put a paper towel over the container. Read our article on Safe Water Bottles and Other Plastics to learn more on the topic.
  • Nix takeout containers. Never microwave food in takeout containers. Styrofoam can melt, and paper containers often have often a greaseproof lining that can leach chemicals into the food. Microwave food in ovenproof glass or ceramic containers.

When shopping, look for

  • Durability and a good warranty. Longer-lasting products cost you less in the long term and keep waste out of landfills and incinerators.
  • The right size. Smaller ovens use less energy (but they also cook less food). Otherwise, there’s little difference in the various products’ energy stats. The government’s Energy Star program doesn’t rate microwaves.

Other Considerations

  • Microwave ovens cost from $70 to $800. Pricier models may have larger capacity, a child lock, sensors to determine when the food is done, “speed cook” technology and browning capability that combine microwaving with other types of heating, and shortcut keys for tasks like bread defrosting and popping popcorn.
  • Microwave ovens have been popular since the early 1970s, yet some people remain concerned about their safety. One common misconception is that food cooked in a microwave becomes radioactive. It does not. As to concerns about microwave leakage, oven manufacturers must comply with the FDA’s regulations, which limit leakage to a level that the FDA says is far below what is known to harm people. Microwave energy drops off dramatically as you move away from the oven. The FDA says that a measurement of radiation made at 20 inches would be 1/100th of the value measured at 2 inches. Although the likelihood of exposure to even low levels of microwaves is extremely low, some people take the extra precaution of not leaning up against the microwave while waiting for the beeps to signal their dinner is ready.

Benefits…

…to you and your health
Microwave energy quickly penetrates deep into food, speeding up cooking time compared with a conventional oven. These ovens’ ability to cook quickly in little or no water also helps food retain its vitamins and minerals. And in the summer, you may appreciate the fact that microwaves don’t heat up the air in the oven, or your kitchen.

…to your wallet
Microwave ovens use much less energy than conventional ovens, so they can save you some pocket change. Let’s assume you are paying 12 cents a kilowatt-hour for your electricity. If you run a medium-size (1,000-watt) microwave at high power for 15 minutes, you’d spend 3 cents. A typical electric oven run at 350 degrees for one hour would cost you 24 cents. Do that every day, and you save yourself $75 a year with the microwave. More significantly, by keeping the kitchen cool in summer, a microwave may reduce your air conditioning costs.

…to the Earth
Microwaving is an energy-efficient way to cook food, but it’s not without its environmental impacts. There are about 27 pounds of steel in the average microwave oven, as well as plastic and glass. And disposing of old units adds to the waste stream.


Common Mistakes

  • Microwaving popcorn. Perfluorooctanoic acid (PFOA), a chemical used to make the lining of many microwave popcorn bags, may be carcinogenic. It’s the same chemical used to make nonstick coatings in cookware and water-repellent fabrics. PFOA is present in the bloodstream of nine out of ten Americans. Major U.S. manufacturers have agreed to phase out their use of the chemical by 2015, but in the meantime you might be safer making your popcorn on the stove, in a pot with a little oil.
  • Superheating water. Be careful when using a microwave to heat water. If it gets too hot, a phenomenon known as “super heating” can occur, in which the water shows no sign of boiling yet is beyond boiling temperature. Disturbing the container even slightly can cause scalding water to erupt. To prevent this safety hazard, check the instruction manual for information about heating times. To greatly reduce the likelihood of superheating, add sugar, tea, or other ingredients to water before heating or wait a minute before removing the container from the oven.

Getting Started

Microwaves are handy, but not essential. If you don’t need one, don’t buy one. And if you have an old one to get rid of, contact your city’s recycling department or Earth911 for local recycling options.

3 Comments

  1. Mimi November 9, 2009
  2. Nikki December 18, 2009
  3. Marsha May 23, 2014

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