Q: Isn’t it unsafe to microwave food in plastic containers?

A: Since stories about the dangers of chemicals leaching from plastic into microwaved food continue to circulate, the Food and Drug Administration has responded to these concerns.

The FDA carefully reviews substances used to make plastics designed for food use. Consumers can be confident that heated meals or leftovers in the microwave are safe. These include microwave-safe plastic coverings that keep food from splattering and microwave-safe containers that contain frozen dinners. Even microwavable popcorn bags, which look like paper, actually contain a metalized plastic film that allows them to reach high temperatures so the corn can fully pop.

Under the food additive provisions of the Federal Food, Drug and Cosmetic Act, new substances used to make plastics for food use are classified as “food contact substances.” They must be found safe for their intended use before they can be marketed.

Edward Machuga, a consumer safety officer in the FDA’s Center for Food Safety and Applied Nutrition, states substances used to make plastics can leach into food; but as part of the approval process, the FDA considers the amount of a substance expected to migrate into food and the toxicological concerns about the particular chemical. The agency has assessed migration levels of substances added to regulated plastics and has found the levels to be well within the margin of safety based on information available to the agency. The FDA will revisit its safety evaluation if new scientific information raises concerns.

One chemical called diethylhexyl adipate has received a lot of media attention. DEHA is a plasticizer, a substance added to some plastics to make them flexible. DEHA exposure may occur when eating certain foods wrapped in plastics, especially fatty foods such as meat and cheese. But the levels are very low. The levels of the plasticizer that might be consumed as a result of plastic film use are well below the levels showing no toxic effect in animal studies.

Other claims have asserted that plastics contain dioxins, a group of contaminants labeled as a “likely human carcinogen” by the Environmental Protection Agency. Machuga says the FDA has seen no evidence plastic containers or films contain dioxins.

Machuga says that consumers should be sure to use plastics for their intended purpose and in accordance with directions. If you don’t find instructions for microwave use, you should use a different plate or container that you know is microwave-safe. Such containers are made to withstand high temperatures.

For example, carryout containers from restaurants and margarine tubs should not be used in the microwave, according to the American Plastics Council. Inappropriate containers may melt or warp, which can increase the likelihood of spills and burns. Also, discard containers that hold prepared microwavable meals after you use them because they are meant for one-time use.

Microwave-safe plastic wrap should be placed loosely over food so that steam can escape, and should not directly touch your food. Some plastic wraps have labels indicating that there should be a one-inch or greater space between the plastic and the food during microwave heating.

Always read directions, but generally, microwave-safe plastic wraps, wax paper, cooking bags, parchment paper, and white microwave-safe paper towels are safe to use. Covering food helps protect against contamination, keeps moisture in, and allows food to cook evenly.

Q: I don’t have any baking powder at home. Can I make my own?

A: There are various substitutions that can be used if you don’t have any baking powder. Here they are:

• Combine one part cornstarch, 1 part baking soda, and two parts cream of tartar
• Or, for one teaspoon baking powder, substitute: 1/3 teaspoon baking soda and 1/2 teaspoon cream of tartar; or 1/4 teaspoon baking soda and 1/2 cup sour milk or buttermilk (decrease liquid called for in recipe by 1/2 cup); or 1/4 teaspoon baking soda and 1/2 tablespoon vinegar or lemon juice used with sweet milk to make 1/2 cup (decrease liquid called for in recipe by 1/2 cup).

Q: How does baking powder work?

A: Unlike baking soda, which needs an acid to create carbon dioxide, baking powder contains an acid to perform this function. By law, baking powder must release a minimum of 12 percent carbon dioxide. There are a variety of acidic compounds that are used in baking powder. They include cream of tartar, monocalcium phosphate, sodium aluminum sulfate, and sodium acid pyrophosphate. The differences lie in how fast they release carbon dioxide. Some baking powders have combinations of these acids.

There are single-acting and double-acting baking powders. Single-acting baking powder is used in commercial bakeries. It contains one acid which dissolves quickly in tap water. It does not require heat.

Because they work quickly, the finished product must be baked immediately after mixing. Baking powder sold in grocery stores is double-acting baking powder. It contains two acids, one that reacts to moisture during mixing to create carbon dioxide and another that reacts to heat during baking. The second reaction is where a majority of the leavening action occurs.