Lots of prepackaged food tells you to use a film lid or to cover your food when you use a microwave. But do you really need to do that?
Is it safe to microwave food without cover?
No, it isn’t always safe to microwave food without cover.
A cover on the container that you put in the microwave keeps steam and heat inside.
If you don’t cover it then the food may not heat to the right temperature to kill all harmful pathogens. This is particularly the case if you are following instructions on the side of a packet or box.
Using a cover also prevents spurts and splats from landing on the inner surface of your microwave. These can build up and cause bacteria to grow which can end up in future meals.
Are you likely to encounter problems if you don’t use a cover? Probably not. But is there a risk, however small, that not using a cover might lead to unsafe conditions and harmful pathogens in your food.
Be smart, use a cover in the microwave. Particularly if you’re reading instructions that tell you to use one.
Reasons why we cover food in the microwave
There are a number of reasons why we use a cover with food in the microwave, here they are along with whether it’s safe to not use a cover.
- Directions on packaged food. The makers of quick ready meals design the cooking instructions to strict specifications to make sure they are fully heated and taste their best as well as being safe for consumption. If you don’t follow the instructions then you can’t guarantee it will be safe. Unsafe
- Dishes that use steam. If you are cooking steamed vegetables in the microwave – a simple and useful tool for the microwave – they will not cook properly if you don’t use a cover as the steam will dissipate throughout the oven rather than be contained in a tight and hot space which cooks the food. Rice is another example of food that cooks a lot better with a cover, even if safety isn’t affected. Safe
- Thawing meat. If the directions for thawing meat say you should cover the food it’s because it traps heat and cooks it quicker. If you don’t do this then the meat may not be fully defrosted and thus may not cook through as it will have cool spots – a real danger with meats in particular. Unsafe
- To prevent splatter on the inside of the microwave. Some foods that you heat in a microwave will burst and pop as they are heated, liquids like soups and curries are really bad for this. This food then ends up on the wall or roof of the microwave and may build up bacteria and other undesirables which may end up in the next dish you or your family uses the microwave for. Unsafe
Should I cover food when reheating?
If you’re doing some general defrosting or reheating – without specific instructions – you might wonder whether you should microwave the food without the cover.
With liquid foods, it’s generally a good idea to cover to spot unhygienic splatters going across the inside of your microwave.
With foods that cook using steam like fish or vegetables, then you definitely should cover. If you don’t do this the food will cook painfully slowly.
With most other foods, it doesn’t make a huge difference, although you may find slightly faster cooking times with a cover, again this is down to the steam that is produced when you heat up your food.
How to cover food in the microwave
The main thing to remember when covering food in a microwave is to make sure there is some kind of vent or hole for steam to escape from.
Microwaves work by heating up the water in your food, turning it into steam. If you cover food then that steam will build up and can cause mini explosions – not ideal.
There’s a reason that film lids are supposed to be pierced when used in microwaves. It’s so steam can be released when you cook your foods, particularly the more liquid ones, and the pressure from the steam will build up and cause mini explosions inside your oven.
Whatever kind of cover you use, make sure there is some way for steam to escape, even if it means the plate is a bit lopsided on your container.
Some specially built containers will have specific steam holes that let steam out, some even have adjustable ones so you can change how much steam is in and so how quickly it cooks. Check some out here.
Do covers on microwaves reflect the waves?
In a word, no. The materials that you should be using for covers are ceramic, glass or plastic. These all mostly let microwaves pass straight through and reflect very little.
This is in contrast to metal which you should never use in a microwave as it reflects large amounts of microwaves.
As such, it is perfectly safe and practical to use covers as it doesn’t affect the waves or the cooking.
Other common safety tips for a microwave
Some of the best safety tips for microwave use. Stay healthy, follow these.
- Use microwavable materials. Glass and ceramic are the safest materials to use in a microwave as the waves themselves will pass straight through. Plastic is good too but only if it says “microwave safe” or equivalent somewhere on them – you don’t want BPA or other plastics leaching into your food. Metals are a big no-no, they cause energy buildup that leads to flashes and mini-explosions.
- Cook foods to safe temperatures. The biggest piece of advice I could give to someone concerned about their or their family’s safety when using the microwave is to always overcook the food then let it stand. For food to be safe, it should be heated to a temperature of 167°F or 75°C. If you can’t use a thermometer then just make sure the food is piping hot and give it 2-3 minutes to stand for the heat to dissipate. High heat kills harmful pathogens that can cause illness or food poisoning.
- Be careful when taking the container out. One of the leading causes of accidents from microwaves is burns caused by people handling containers that are too hot or spilling them because they can’t hold the container. A quick test of how hot the container is, using the back of your hand, goes a long way.
- Spread your food out. The biggest reason why you will get cool or even icy spots in your food is because the food is thick or dense. Microwaves can only penetrate 1-2 cm into food so if you’re cooking a big plate of something then try to spread the food out so the heat gets evenly distributed rather than burning the outside and leaving the interior icy cold.