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Microwave Oven FAQ's

General Operations

Safety of Microwave Ovens (General)

Cooking Safely with a Microwave Oven

Cooking Container Questions


 

General Operations

Q:

 

What is microwave radiation?

 

 

 

 

 

 

 

Microwaves are a form of "electromagnetic" radiation; that is, they are waves of electrical and magnetic energy moving together through space. Electromagnetic radiation ranges from the energetic x-rays to the less energetic radio frequency waves used in broadcasting. Microwaves fall into the radio frequency band of electromagnetic radiation. Microwaves should not be confused with x-rays, which are more powerful.

Microwaves have three characteristics that allow them to be used in cooking: they are reflected by metal; they pass through glass, paper, plastic, and similar materials; and they are absorbed by foods.

Source: U.S. Food and Drug Administration, Center for Devices and Radiological Health Consumer Information.

Web site: http://www.fda.gov/cdrh/consumer/microwave.html 

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Q:

 

How do microwave ovens work?

 

Inside every microwave oven is a device called a magnetron, which converts electrical power into very short (micro) radio waves that penetrate food to a depth dependent on the wavelength of the oven and the properties of the food. These waves are readily absorbed by water, fats and sugars, resulting in very fast vibrations. The friction between these rapidly moving food molecules, in turn, creates heat. On high power, food is subjected to the maximum amount of microwave energy. To produce a power level less than 100 percent, the magnetron cycles on and off. For example, at 50 percent power the magnetron is on only 50 percent of the time. Even when microwaves are not being emitted (while cycling off or when turned off), the vibrations of the food molecules continue, and may even lead to an increase in temperature, continuing the cooking process. Cooking instructions provided on packaging often account for this effect and recommend a “standing time” after the microwave has turned off. 

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Q:

 

Are there cooking or household operations for which the microwave oven should not be used?

 

Microwave ovens should NOT be used for deep-frying, canning, or heating baby bottles. There are not adequate temperature controls for these functions to be safely performed in a microwave oven.

Due to the risk of fire, microwave ovens should not be used to dry or sterilize clothing or other non-food articles.

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Q:

 

Do microwaves cook food from the inside out?

 

No. Microwaves penetrate the food to a depth of 1 to 1½ inches. In thicker pieces of food, the microwaves don't reach the center. That area would cook by conduction of heat from the outer areas of the food into the middle.

In a microwave oven, the air in the oven is at room temperature so the temperature of the food surface is cooler than food in a conventional oven where the food is heated by hot air. Therefore, food cooked in a microwave oven doesn't normally become brown and crispy.

Source: U.S. Department of Agriculture, Food Safety and Inspection Service

U.S. Food and Drug Administration, Center for Food Safety and Applied Nutrition.

Web site: http://www.foodsafety.gov/~fsg/fs-mwave.html

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Q:

 

Why are little “lightning bolts” and sparks shooting around in my microwave?

 

Operating a microwave oven while metallic objects are in the cooking cavity disrupts the microwave energy pattern and produces a condition called “arcing”. Just as the air between a thundercloud and the earth can become charged or ionized, the air between two metal objects within a microwave oven will get electrically charged. An arc occurs when electric current moves through this ionized air like a small bolt of lightning connecting the gap between the metal objects.

In addition to happening when microwaves react to gold paint on dishes, twist ties, or other metallic objects, arcing inside the microwave oven can also occur when some foods such as raw carrots or hotdogs are being cooked. In hot dogs, this can be due to the uneven mixing of salts and additives. In carrots, it can be due to the minerals in the soil in which they were grown. Whatever the cause of the arcing, it is recommended that the oven be turned off immediately to end the sparks. Prolonged arcing can damage the oven and/or the utensil. If caught at once, arcing should not damage the oven. Remove the offending utensil or food from the oven and either substitute a microwave-safe utensil or cook the food by other methods.

Source for second paragraph: U.S. Department of Agriculture, Food Safety and Inspection Service.

Web site: USDA Fact Sheets - Microwave Ovens and Food Safety

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Q:

 

Does cooking food in a microwave oven rob it of its nutritional value?

 

Microwave-cooked food may actually retain vitamins and minerals better than stove-top-cooked food because the microwave zaps food quickly and without much water. The longer you cook food in liquid, the more nutrients may seep out, which is fine for soups and stews, but it's a problem if you discard the liquid before eating. One study found that spinach retained all of its folate when cooked in a microwave, compared with 77 percent when cooked on a stove.

Source: ConsumerReports.org – Microwave Safety

Web site: http://www.consumerreports.org/cro/appliances/kitchen-appliances/microwave-ovens/microwave-safety-9-06/overview/0609_microwave-safety_ov.htm

Using a microwave oven to cook food, although sometimes considered an “easy way out,” has many benefits. The traditional method of covering with water and boiling vegetables leads to loss of vitamins and minerals due to leaching into the water. This is especially true for water-soluble vitamins such as vitamins C and thiamin. Microwaving with only a small amount of water in a microwave-safe container, which minimizes the surface contact between the vegetables and the water, along with a reduced cooking time, ensures that higher levels of vitamins will be retained.

Since prolonged heat destroys many vitamins and other beneficial compounds, cooking or reheating food quickly in a microwave retains more nutrients than heating food over a long period of time by a more conventional method.

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Q:

 

Can microwave ovens be operated empty?

 

Some ovens should not be operated when empty. Refer to the instruction manual for your oven.

Source: U.S. Food and Drug Administration, Center for Devices and Radiological Health Consumer Information.

Web site: http://www.fda.gov/cdrh/consumer/microwave.html

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Q:

 

How should microwave ovens be cleaned?

 

Clean the oven cavity, the outer edge of the cavity, and the door with water and a mild detergent. A special microwave oven cleaner is not necessary. Do not use scouring pads, steel wool, or other abrasives.

Source: U.S. Food and Drug Administration, Center for Devices and Radiological Health Consumer Information.

Web site: http://www.fda.gov/cdrh/consumer/microwave.html

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Safety of Microwave Ovens (General)

 

Q:

 

How do I know microwave ovens are safe?

 

The Food and Drug Administration (FDA) has the responsibility for carrying out an electronic product radiation control program mandated by the Electronic Product Radiation Control provisions of the Food Drug and Cosmetic Act. Through its Center for Devices and Radiological Health, FDA sets and enforces standards of performance for electronic products to assure that radiation emissions do not pose a hazard to public health.

A Federal standard limits the amount of microwaves that can leak from an oven throughout its lifetime to 5 milliwatts (mW) of microwave radiation per square centimeter at approximately 2 inches from the oven surface. This limit is far below the level known to harm people. Microwave energy also decreases dramatically as you move away from the source of radiation. A measurement made 20 inches from an oven would be approximately one one-hundredth of value measured at 2 inches.

The standard also requires all ovens to have two independent interlock systems that stop the production of microwaves the moment the latch is released or the door opened. In addition, a monitoring system stops oven operation in case one or both of the interlock systems fail. The noise that many ovens continue to make after the door is open is usually the fan. The noise does not mean that microwaves are being produced. There is no residual radiation remaining after microwave production has stopped. In this regard a microwave oven is much like an electric light that stops glowing when it is turned off.

All ovens must have a label stating that they meet the safety standard. In addition, FDA requires that all ovens have a label explaining precautions for use. This requirement may be dropped if the manufacturer has proven that the oven will not exceed the allowable leakage limit even if used under the conditions cautioned against on the label.

Source: U.S. Food and Drug Administration, Center for Devices and Radiological Health Consumer Information.

Web site: http://www.fda.gov/cdrh/consumer/microwave.html 

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Q:

 

Is it safe to be around an operating microwave oven?

 

Yes, but there are some unknowns (as there are with operating conventional ovens) and some precautions that can minimize any danger.

Much research is under way on microwaves and how they might affect the human body. It is known that microwave radiation can heat body tissue the same way it heats food. Exposure to high levels of microwaves can cause a painful burn. The lens of the eye is particularly sensitive to intense heat, and exposure to high levels of microwaves can cause cataracts. Likewise, the testes are very sensitive to changes in temperature. Accidental exposure to high levels of microwave energy can alter or kill sperm, producing temporary sterility. But these types of injuries - burns, cataracts, temporary sterility - can only be caused by exposure to large amounts of microwave radiation, much more than the 5mW limit for microwave oven leakage.

Less is known about what happens to people exposed to low levels of microwaves. Controlled, long-term studies involving large numbers of people have not been conducted to assess the impact of low level microwave energy on humans. Much research has been done with experimental animals, but it is difficult to translate the effects of microwaves on animals to possible effects on humans. For one thing, there are differences in the way animals and humans absorb microwaves. For another, experimental conditions can't exactly simulate the conditions under which people use microwave ovens. However, these studies do help us better understand the possible effects of radiation.

FDA continues to enforce radiation protection requirements because many scientific questions about exposure to low-levels of microwaves are not yet answered. Consumers should take certain common sense precautions, such as never use a microwave with faulty hinges or a door that does not fit properly. It is also known that microwaves disperse and dissipate very quickly into the atmosphere. This means maintaining a distance of 20 inches away from an operating microwave oven is always a good safety measure.

Source: U.S. Food and Drug Administration, Center for Devices and Radiological Health Consumer Information.

Web site: http://www.fda.gov/cdrh/consumer/microwave.html

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Q:

 

Do microwave ovens cause cancer?

 

To date, there is no scientific evidence linking microwave ovens and cancer. Intense microwave radiation can cause burns, temporary sterility, and cataracts, since it can heat body tissue just as it heats food. However, to be injured by microwave radiation, you would have to be exposed to levels that are much higher than the allowable limits for leakage on newer ovens.

Source: ConsumerReports.org – Microwave Safety

Web site: http://www.consumerreports.org/cro/appliances/kitchen-appliances/microwave-ovens/microwave-safety-9-06/overview/0609_microwave-safety_ov.htm

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Q:

 

Does cooking food in a microwave oven make it radioactive?

 

Food cooked in a microwave oven does not present a radiation risk. Microwaves cease to exist as soon as the power to the magnetron of a microwave oven is switched off. They do not remain in the food and are incapable of making either it or the oven radioactive.

Source: Microwave Safety, a concise guide and summary.

Web site: http://www.microwavecooking.com/Microwave_Safety.htm

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Q:

 

Have radiation injuries resulted from microwave ovens?

 

There have been allegations of radiation injury from microwave ovens, but none as a direct result of microwave exposure. The injuries known to FDA have been injuries that could have happened with any oven or cooking surface. For example, many people have been burned by the hot food, splattering grease, or steam from food cooked in a microwave oven.

Source: U.S. Food and Drug Administration, Center for Devices and Radiological Health Consumer Information.

Web site: http://www.fda.gov/cdrh/consumer/microwave.html

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Q:

 

Is there a danger of microwave leaking radiation?

 

There is little cause for concern about excess microwaves leaking from ovens unless the door hinges, latch, or seals are damaged. In FDA's experience, most ovens tested show little or no detectable microwave leakage. If there is some problem and you believe your oven might be leaking excessive microwaves, contact the oven manufacturer, a microwave oven service organization, your state health department, or the nearest FDA office.

Source: U.S. Food and Drug Administration, Center for Devices and Radiological Health Consumer Information.

Web site: http://www.fda.gov/cdrh/consumer/microwave.html

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Q:

 

Do microwave ovens affect pacemaker performance?

 

At one time there was concern that leakage from microwave ovens could interfere with certain electronic cardiac pacemakers. Similar concerns were raised about pacemaker interference from electric shavers, auto ignition systems, and other electronic products. FDA does not specifically require microwave ovens to carry warnings for people with pacemakers. The problem has been largely resolved because pacemakers are now designed to be shielded against such electrical interference. However, patients with pacemakers may wish to consult their physicians if they have concerns.

Source: U.S. Food and Drug Administration, Center for Devices and Radiological Health Consumer Information.

Web site: http://www.fda.gov/cdrh/consumer/microwave.html

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Cooking Safely With a Microwave Oven

 

Q:

What is the best way to cook with a microwave oven?

 

The shape and consistency of food affects how evenly they heat in microwave ovens. Food with symmetrical shapes, especially round or oval, and with even thickness (less that 1 inch) generally heat the most uniformly. For thicker portions, better results may be obtained with reduced power for longer periods such that the outer portions don’t overcook before the center is heated thoroughly. To promote uniform cooking, arrange food items evenly in a covered dish and add some water, if the food is fairly dry, to promote more even absorption of microwaves. Bone can shield meat from thorough cooking, so, where possible, debone large pieces of meat. It is important that foods be stirred, rotated, and inverted, if possible, halfway through cooking for more even distribution of microwaves and heat throughout the food. Even if a turntable is used, it is best to place the food off-center and to stir foods top to bottom or turn foods over, if possible.

Use microwave-safe containers. Do not use foam containers for cooking or reheating foods unless labeled microwave-safe. Cover the dish with a lid, microwave-safe plastic wrap, or a clean, unprinted, white paper towel, but leave a small opening for steam to escape. Allow enough space between the food and the plastic wrap so the wrap doesn’t touch the food. The steam that is created by using a lid will help heat the food more evenly and will also help destroy any harmful bacteria.

Just as other types of ovens, microwave cooking can destroy bacteria and other pathogens; however, food can cook less evenly than in conventional ovens, resulting in cold spots, due to factors described earlier. For best results in both the quality and safety of frozen or refrigerated foods, consumers should follow the cooking instructions on product labels and observe the standing times, if provided. Adjustments to the cooking time, due to oven wattage or other factors, may be necessary to reach the desired temperature before serving. For frozen or refrigerated foods that do not have labeled cooking instructions, it is suggested that the following cooking temperatures—as recommended by the United States Department of Agriculture (USDA)—be reached in all parts of the food.

· Ground meats: 160° F (71° C)

· Ground poultry: 165° F (74° C)

· Beef, veal, and lamb steaks, roasts, and chops: 145° F (63° C)

· All cuts of fresh pork: 160° F (71° C)

· Poultry: 165° F (74° C)

· Eggs and dishes containing eggs (i.e. casseroles, soufflés, etc.): 160° F (71° C)

· Fish/seafood: 145° F (63° C)

· Foods to be reheated that have previously been cooked and cooled by the consumer (i.e. leftovers): 165° F (74° C)

After the cooking time has ended and proper standing time has been allowed, the temperature of the food should be checked. Remove the food from the microwave and use a food thermometer to check the food in several places to ensure that a safe temperature has been reached throughout. Keep in mind all microwave ovens vary in power.

* Do not leave the thermometer in the food while microwaving, unless the thermometer is labeled as safe for microwave use, as this may result in arcing and could be a potential fire hazard. 

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Q:

 

What is the best way to defrost food using a microwave?

 

When defrosting packaged store-bought foods, check the label for microwave defrosting instructions. For foods with no instructions provided, remove food from its packaging before defrosting and place in a microwave-safe container, covered with a lid or plastic wrap. Refer to the microwave user manual, if available. If not, select the “defrost” setting or 30 percent power and set the time according to the size and amount of food to defrost. Without specific guidance, it is a good idea to test the progress by using a knife or fork to pierce the food and feel for frozen spots every minute or so until the food is completely defrosted. Also, while defrosting, rotate, stir or turn food upside down where possible, and for individual pieces, such as chicken parts, break them apart. When thawing ground meats, as the meat softens, scrape it from the frozen mass and remove it from the oven. Continue this process, as often as necessary, to properly thaw the meat.

Cook meat, poultry, egg-containing dishes, and fish immediately after defrosting. Hold or store these foods at refrigeration temperatures (less than 41° F; 5° C) to prohibit the growth of hazardous bacteria, which may cause illness even if the food is cooked thoroughly at a later time.

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Q:

 

What are cold spots and are they dangerous?

 

Microwave ovens can cook unevenly and leave "cold spots," where food has not been thoroughly cooked and harmful bacteria can survive.

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Q:

 

What can be done to prevent cold spots and the possibility of foodborne illnesses?

 

The possibility of foodborne illnesses may be minimized by following these microwave cooking suggestions and ensuring food is thoroughly cooked:

Arrange food items evenly in a covered dish and add some liquid if needed. Cover the dish with a lid or plastic wrap; loosen or vent the lid or wrap to let steam escape. The moist heat that is created will help destroy harmful bacteria and ensure uniform cooking. Cooking bags also provide safe, even cooking.

Do not cook large cuts of meat on high power (100%). Large cuts of meat should be cooked on medium power (50%) for longer periods. This allows heat to reach the center without overcooking outer areas.

Stir or rotate food midway through the microwaving time to eliminate cold spots where harmful bacteria can survive, and for more even cooking.

When partially cooking food in the microwave oven to finish cooking on the grill or in a conventional oven, it is important to transfer the microwaved food to the other heat source immediately. Never partially cook food and store it for later use.

Use a food thermometer or the oven’s temperature probe to verify the food has reached a safe temperature. Place the thermometer in the thickest area of the meat or poultry—not near fat or bone—and in the innermost part of the thigh of whole poultry. Cooking times may vary because ovens vary in power and efficiency. For frozen or refrigerated foods that do not have labeled cooking instructions, it is suggested that the following cooking temperatures—as recommended by the United States Department of Agriculture (USDA)—be reached in all parts of the food.

· Ground meats: 160° F (71° C)

· Ground poultry: 165° F (74° C)

· Beef, veal, and lamb steaks, roasts, and chops: 145° F (63° C)

· All cuts of fresh pork: 160° F (71° C)

· Poultry: 165° F (74° C)

· Eggs and dishes containing eggs (i.e. casseroles, soufflés, etc.): 160° F (71° C)

· Fish/seafood: 145° F (63° C)

· Foods to be reheated that have previously been cooked and cooled by the consumer (i.e. leftovers): 165° F (74° C)

After the cooking time has ended and proper standing time has been allowed, the temperature of the food should be checked. Remove the food from the microwave and use a food thermometer to check the food in several places to ensure that a safe temperature has been reached throughout. Keep in mind all microwave ovens vary in power.

Cooking whole, stuffed poultry in a microwave oven is not recommended. The stuffing might not reach the temperature needed to destroy harmful bacteria.

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Q:

 

What is superheating?

 

The FDA received reports in the past of serious skin burns or scalding injuries around people's hands and faces as a result of hot water erupting out of a cup after it had been over-heated in a microwave oven. Over-heating of water in a cup can result in superheated water (water heated past its boiling temperature), which does not appear to be boiling.

This type of phenomena occurs if water is heated in a clean cup. If foreign materials such as instant coffee or sugar are added before heating, the risk is greatly reduced. If superheating has occurred, a slight disturbance or movement such as picking up the cup, or pouring in a spoon full of instant coffee, may result in a violent eruption with the boiling water exploding out of the cup.

Source: U.S. Food and Drug Administration, Center for Devices and Radiological Health Consumer Information.

Web site: http://www.fda.gov/cdrh/consumer/microwave.html

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Q:

 

What can be done to avoid super-heated water?

 

Users should follow the precautions and recommendations found in the microwave oven instruction manuals, specifically the heating time. Users should not use excessive amounts of time when heating water or liquids in the microwave oven. Determine the best time setting to heat the water to the desired temperature and use that time setting regularly.

Source: U.S. Food and Drug Administration, Center for Devices and Radiological Health Consumer Information.

Web site: http://www.fda.gov/cdrh/consumer/microwave.html

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Q:

 

Is it safe to cook using plastic dishes in a microwave?

 

When heated, chemicals can be released from some plastic packaging materials.

When cooking with plastics, it is best to follow the directions stated in your microwave instruction manual and only use plastics specifically designated as safe for microwave cooking

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Cooking Container Questions

Q:

 

Are there dishes or containers that should not be used in microwave cooking?

 

For differing reasons, the following should NOT be used in a microwave:

  • Cold storage containers: margarine tubs, cottage cheese and yogurt cartons, etc. These materials are not approved for cooking and chemicals can migrate into food.
  • Brown paper bags and newspapers.
  • Metal pans.
  • Foam-insulated cups, bowls, plates or trays.
  • China with metallic paint or trim.
  • Chinese "take-out" containers with metal handles.
  • Metal "twist ties" on package wrapping.
  • Food completely wrapped in aluminum foil.
  • Food cooked in any container or packaging that has warped or melted during heating.

Instructions accompanying each microwave oven often contain a list of recommended containers for safe use. They also often provide instructions on how to test containers to determine whether or not they can safely be used in microwave ovens.  

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Q:

 

What containers are best to use when cooking with a microwave oven?

 

Only use cookware that is specially manufactured for use in the microwave oven. Glass, ceramic containers, and all plastics that are safe to use usually will be labeled for microwave oven use.

SAFE TO USE:

  • Any utensil labeled for microwave use.
  • Heatproof glass (such as Pyrex, Anchor Hocking, etc.).
  • Glass-ceramic (such as Corning Ware).
  • Oven cooking bags.
  • Baskets (straw and wood) for quick warm-ups of rolls or bread. Line the basket with napkins to absorb moisture from food.
  • Most paper plates, towels, napkins and bags. For optimal safety use white, unprinted materials.
  • Wax paper, parchment paper, heavy plastic wrap. Do not allow plastic wrap to touch food; vent it to allow a steam escape.
  • Heat-susceptor packaging.

Source: U.S. Department of Agriculture, Food Safety and Inspection Service
U.S. Food and Drug Administration, Center for Food Safety and Applied Nutrition.
Web site: http://www.foodsafety.gov/~fsg/fs-mwave.html

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Q:

 

Is it true that microwaving with plastic releases cancer causing dioxins into the food?

 

No. A popular Web rumor wrongly contends that plastics contain dioxins, which are a likely carcinogen. Some plastic wraps may, however, contain chemical plasticizers that add flexibility, and those can migrate into food when heated. The risks associated with consuming trace amounts of plasticizers are small. But more research is needed, so leave space between plastic wrap and food, or use a paper towel to cover your food instead. (Note that plastic containers not approved for microwave use can warp and leak potentially hazardous chemicals into the food.)

Source: ConsumerReports.org – Microwave Safety

Web site: http://www.consumerreports.org/cro/appliances/kitchen-appliances/microwave-ovens/microwave-safety-9-06/overview/0609_microwave-safety_ov.htm

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