Why plastic containers are no-no in microwaves
Feb 11 2013
A microwave works by dielectric heating, which uses electromagnetic radiation. It passes non-ionising microwave radiation through the food. They heat food very fast, as compared with regular ovens or cooking with gas.
According to health.edu, microwave ovens cook food with waves of oscillating electromagnetic energy that are similar to radio waves but move back and forth at a much faster rate. These quicker waves are remarkably selective, primarily affecting molecules that are electrically asymmetrical — one end positively charged and the other negatively so. Water is a polar molecule, so when a microwave oven cooks or heats up food, it does so mainly by energising — which is to say, heating up — water molecules, and the water energises its molecular neighbours.
The main argument against using a microwave to cook or heat food is the supposed loss of nutrients from the food. But supporters of microwaves say that the loss of nutrients takes place depending on the method of cooking. The maximum loss of nutrients happens when food is boiled, as the vegetables lose their goodness into the water. Unless that water is utilised, the quantum of minerals and antioxidants leached forever from the vegetable. This loss can happen whether one uses a microwave or a gas top to cook.
Harward.edu experts state that an Italian research in 2008 compared three cooking methods — boiling, steaming, and frying — and the effect they had on the nutritional content of broccoli, carrots and zucchini. Boiling carrots actually increased their carotenoid content, while steaming and frying reduced it. This could be because it takes longer for vegetables to get tender when they’re steamed, so the extra cooking time results in more degradation of some nutrients and longer exposure to oxygen and light. The US food and drug administration (USFDA) regulates microwave manufacturing with safety standards for reducing human exposure to radiation.
Many glass or plastic containers do not absorb enough microwaves to become hot during cooking. In fact, “microwave safe” glass, plastic or ceramic cookware allows most of the microwave energy to pass safely through to the food within. In contrast, metal objects reflect the microwave energy back within the oven cavity and may spark a potentially damaging electrical discharge.
Plastic contains a number of potentially harmful chemical additives. The heat of a microwave can cause those chemicals to leach into your food. One chemical of concern is bisphenol A or BPA. Some scientific research suggests exposure to BPA can increase one’s risk of certain types of cancer. However, in 2012, the FDA ruled that more evidence would be needed to substantiate these claims. As a precaution, the FDA advises consumers to avoid adding hot liquids to plastics containing BPA.
Another item of concern is plastic wrap (or cling film). There have been cases of people using plastic wrap to heat up food in a microwave. At room temperatures, its usage can be fine, but in a micro wave, it gets exposed to intense heat, which causes its components to leach into your food.
In order to use a microwave safely, only use containers that are labeled “microwave-safe” as per the manufacturer’s instructions. The international symbol for a microwave safe container is three wavy lines, on top of each other.
Utensils that are safe for microwave use include those made from heat proof glass, glass ceramic cookware, oven cooking bags, straw and wood baskets (for quick heating of bread rolls or buns) lined with napkins to absorb moisture from the food, and those labeled safe for microwave use. Always cover the food when using the microwave with a microwave safe lid.
Avoid using plastics, chinaware which has any metallic paint on it or even any metallic design, Styrofoam cups or glasses, aluminium foil and any container, which is not marked as safe for use in a microwave.
Under certain circumstances, it can be safe to use small amounts of aluminum foil in a microwave oven. However, always consult the owner’s manual of your particular microwave oven and follow the manufacturer’s recommendations for aluminum foil. zz
(The writer is the owner of wellness centre Back to the Basics and the author of The Vegan Kitchen: Bollywood Style!)