FAQs: Using Plastics in the Microwave

FAQs: Using Plastics in the Microwave Image

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Because plastics serve so many purposes in the kitchen, many consumers get confused about which products are right for the microwave. This list of FAQs will help you decide which plastics to use and how to use them properly.


How can I know if a plastic container is okay to use in the microwave oven?

Many of today’s plastic containers, packages and wraps are specially designed to withstand microwave temperatures. To make sure yours is one of them, check the item or its packaging label and follow any instructions. If neither the item nor the package is marked, it’s best to use a different container.

Some products may use the term “Microwave Safe.” This is the manufacturer’s way of letting consumers know that a product has been designed to withstand microwave heat without melting or warping under normal use conditions. Other products may carry a microwave symbol or simply provide instructions for proper microwave use. Either of these is an indication that a product is suitable for microwaving when used in accordance with the directions provided.

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Are other plastic items unsafe to use in the microwave?
All plastics intended for food use — whether designed for microwaving or not — must meet stringent U.S. Food and Drug Administration (FDA) safety standards before they are allowed on the market. When manufacturers develop individual plastic packaging products, they often conduct additional testing based on a product’s intended use. Choosing to microwave with a plastic item not labeled for microwave suitability isn’t necessarily “unsafe,” but you won’t have the assurance of knowing the item was tested and evaluated for this purpose.

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Can knowing the type of plastic something is made from help me decide whether I should use a plastic container or package in the microwave?
Many plastic food packages are marked with a symbol that identifies a particular type of plastic for recycling purposes. This symbol is not intended to provide guidance on safe or recommended uses. The only way to know if a particular item is suitable for microwave use is to check the label.

For example, frozen meals are often packaged in microwavable trays made of PET, a type of plastic also used to make cold storage jars and beverage bottles. While microwavable PET trays are specially fabricated for high heat resistance, other packages made with PET could warp if subject to high heat.

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What should I know about microwaving with plastic wrap?
Plastic wrap, placed loosely over bowls or dishes during reheating, can help retain moisture to allow foods to cook more evenly and thoroughly and prevent splattering. As with any plastic packaging, it’s best to use plastic wrap that is labeled for microwave use or includes microwave cooking instructions. Because microwaves heat foods more quickly than plastic, most manufacturers recommend leaving at least an inch between the food and the wrap covering the dish. This is to prevent the plastic wrap from melting, which could result from contact with extremely hot foods.

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Is it okay to use plastic wrap with high-fat foods in the microwave?
Yes, it is okay to use plastic wrap with high-fat foods in accordance with the manufacturer’s instructions. Plastic wrap is not heated by microwave energy, but it can be heated by contact with hot foods. Normally, foods in a microwave oven do not become hot enough to bring the wrap to its melting point. However, because certain foods with high fat content (such as butter) can become very hot in a microwave oven, most manufacturers recommend leaving an inch of air space between the food and the wrap or turning back a corner for ventilation. The instructions on various plastic wraps may vary, so again, it’s always a good idea to check the label.

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Is it safe to reheat leftovers in takeout containers or reused containers, such as empty butter tubs or dessert topping containers?
It is not likely that microwaving with these containers presents any health risk, but if used inappropriately, accidental burns could occur. So, unless a container is marked that it is suitable for microwave use, there may be a risk that it will melt or deform if exposed to high heat. If your container isn’t marked for microwave use, it’s best to choose one that is.

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I got an e-mail from Johns Hopkins alleging that microwaving food in plastic containers releases dioxin. Is this true?
No. This is an e-mail hoax that has been circulating the Internet for years. Dioxins are a group of compounds that can be produced by combustion at very high temperatures. The vast majority of plastics used in food wraps and packaging do not contain the chemical constituents needed to form dioxins. And dioxins form at very high temperatures, typically above 700 degrees Fahrenheit — much higher than the temperatures that would be generated by microwave cooking. You also may hear claims that using plastic containers in the freezer can “release” dioxins — which is also untrue. According to the FDA, which regulates food packaging, “With regard to dioxins, we have seen no evidence that plastic containers or films contain dioxins and know of no reason why they would.”

The e-mail and its alleged ties to Johns Hopkins University or Walter Reed Army Medical Center (depending on which version you receive) are part of the hoax, and both organizations have publicly disavowed the claims.

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