Q: Is it unsafe to microwave food in some plastic containers?
The straight answer: yes
The facts: unless you are using a microwave-safe variety, it is not safe to microwave your food in regular plastic containers and wraps. Dr Alex Ching, a radiologist at Matilda International Hospital, says plastic containers may be safe to hold foods at room temperature, but advises against using them in microwave ovens.
Typically made from high-density polyethylene, these containers should be avoided for heating up foods with a high fat and sugar content.
Such foods may reach temperatures exceeding 100 degrees Celsius in the microwave, and the high temperature can cause the plastic chemicals to break down and leach out, thereby contaminating the food in the container.
Microwaveable or microwave-safe containers are commonly made from polypropylene and crystalline polyethylene terephthalate (CPET). These materials have high melting points (above 200 degrees) and are therefore safe, says Ching.
Recognising the potential for chemicals in plastic to migrate, the Food and Environmental Hygiene Department closely regulates the production of plastic containers and materials that come into contact with food.
There are stringent rules that the manufacturers of food packaging must comply with.
Before issuing its "microwave safe" stamp of approval, the department estimates the ratio of plastic surface area to food, how long the container is likely to be in the microwave, how often a person is likely to eat from the container, and how the food is expected to cook while microwaving.
The scientists then measure the chemicals that leach out and the extent to which they migrate to foods.
Manufacturers have to undertake a toxicological evaluation to show that those levels are safe.
In this context, the term "safe" means that the material has to pass a test that shows it will not cause cancer or genetic damage, or have an impact on reproduction or development. Only containers that pass this test can display the words "microwavable", "microwave-safe", or their equivalents, adds Ching.
Such containers are typically tested for up to 240 hours in the microwave.
"Therefore, if you were to buy a reusable, microwave-safe plastic container and use it to microwave your food, you should feel quite confident about using it, as long as you follow the instructions."
Avoid microwaving plastic containers such as those used for takeaways, or those used to hold margarine or yogurt.
Ching also warns not to microwave plastic storage bags or any other plastic containers that have been designated for other purposes. If you are concerned, just transfer the food to a microwave-friendly glass or ceramic container.