Microwave Ovens and Food Safety Issues

by Health Canada

Many Canadians use microwave ovens as a convenient way to thaw, cook and reheat food. A number of people have concerns, however, about the effect of microwaves on their health and on the health and safety of their foods.

Many people who use microwave ovens say they are going to "nuke" their food. This reference to nuclear energy is incorrect and misleading. Microwaves are a form of radiofrequency electromagnetic energy. They are generated electronically. They do not come from radioactive sources and they do not cause food or the oven itself to become radioactive.

When microwaves penetrate food, they cause water molecules in the food to rotate. The rotation causes friction between the molecules and the result is a rapid rise in temperature. This is why the cooking time with microwave ovens is shorter than with conventional ovens. When you shut the microwave oven off, the microwaves disappear.

Health and Safety Concerns Associated With Microwave Cooking

Some microwave energy may leak from your oven while you are using it, but this would pose no known health risks, as long as the oven is properly maintained.

Microwaves do not change the chemical components of in food and so the formation of new compounds, like carcinogens, is not expected. Some studies have been conducted to investigate any possible negative health effects of microwaving foods. These studies, which have been reviewed by Health Canada scientists, have found no evidence of toxicity or carcinogenicity.

In general, the health and safety concerns associated with microwave cooking are similar to the issues involved with other cooking methods, such as conventional ovens, stove-top cooking and grilling. For example, all cooking methods have some effect on the nutrients in food. The effect is worse if you over-cook the food. Microwave cooking tends to be less harsh on nutrients than conventional cooking methods, because the cooking times are shorter and less water is used. To help preserve nutrients when microwaving food, use techniques that promote the even distribution of heat. This will help prevent the formation of "hot spots" where portions of the food could be over-cooked. Steps to promote even heating are outlined in the Minimizing Your Risk section below.

There is no simple answer to questions about which cooking method is best for retaining nutrients. Research into the subject is ongoing. From a health perspective, there is no reason to use any one cooking method exclusively.

Other concerns associated with all methods of cooking, including microwave cooking, are foodborne illness and burns.

Minimizing Your Risk

Foodborne Illness

Raw food of animal origin, such as meats, seafood, poultry and eggs (including juices and drippings) may carry disease-causing bacteria. No matter which cooking method you use, the risk that bacteria will multiply and cause foodborne illness increases when foods are allowed to sit at temperatures in the "danger zone" between 4o C and 60o C (40° F to 140° F) for more than 2 hours. To minimize the risk of foodborne illness:

When handling raw foods of animal origin, always chill promptly.

Clean your hands and kitchen surfaces often.

Keep foods separate and do not cross-contaminate.

Cook food thoroughly.

If you use the microwave oven to defrost or partially cook food, be sure to refrigerate or finish cooking the food by some other method right away. Do not let perishable foods linger in the vdanger zone" for longer than 2 hours.

Take steps to ensure that the microwave oven heats food evenly and does not leave underheated areas (cold spots) where bacteria might multiply and cause food poisoning. You can promote even heating in the microwave oven by:

• cutting food into small pieces for uniform cooking
• arranging items in a uniform manner
• adding a liquid (such as water, juice or gravy) to solid foods
• stopping part way through cooking to stir foods or rotate trays or containers
• covering food with a microwave-safe lid or with microwave-safe plastic wrap to trap steam
• following directions for "standing times". This helps ensure that heat is distributed uniformly, even after cooking.

About the Author

www.hc-sc.gc.ca
Health Canada is the Federal department responsible for helping Canadians maintain and improve their health, while respecting individual choices and circumstances.