What Can Not Go In A Microwave?

When microwaves were first introduced into homes during the late 1960s they received a lot of scepticism. There were many rumours that microwaves could cause harm and increase the risk of illness.

As the technology progressed and more tests were done it was learned that microwaves were in fact, safe for use as long as you kept within certain guidelines. In this article I look at microwave cooking and list all of the things that are definitely unsafe to put in the microwave.

Keep reading to find out more.

What Containers Should You Not Use In A Microwave?

person taking hot food out a microwave

Let’s start with the materials used to make the containers you’re most likely to use in the microwave. Many containers are microwave safe but the only way you can be sure is if the container has the microwave safe symbol which looks like three wavy lines.

Sometimes the wavy lines are shown inside a microwave or there will be three wavy lines on their own. As long as the container has the microwave safe symbol or states “microwave safe” on the packaging or on the bottom of the container, it’s considered safe to use in the microwave whilst cooking or heating up food.

Can You Microwave Plastic?

plastic bottles and cups

There are many plastic plates, bowls, cups or even jugs that are ideal for using in the microwave. You need to check for the microwave safe symbol but any that have that symbol or state “microwave safe” can be used in a microwave.

If the plastic container doesn’t say microwave safe or display the three wavy lines, then it’s not safe to use in a microwave. There are a few problems with using non microwave safe plastics to heat food or drinks in the microwave. Which include;

The Container Might Melt

One of the main problems with using non microwave safe plastics in the microwave is they are not strong enough to withstand the high temperatures and can lose their integrity.

This leads to the plastic starting to melt and lose its shape. Leading to whatever food is in the container spilling all over the microwave. If the plastic itself is allowed to melt and reach the sides or base of the appliance, it will stick to the surface and every time you use the appliance it will smell of burning plastic.

Harmful Chemicals Found In The Plastic Can Leach Into Food

The plastic container melting is only part of the problem. Unfortunately there are far more serious consequences of using non microwave safe plastics to heat food or drinks.

Many plastics are made from a number of chemicals, one of which is Bisphenol A (BPA). BPA has been extensively researched by the scientific community and has been linked to many serious health conditions.

BPA is a weak synthetic oestrogen and when it enters the human body it can disrupt hormones. Any plastic that contains BPA or its so-called safer replacements BPS and BPF have been linked to cancer, cardiovascular diseases, reproductive problems, obesity and diabetes.

Single use plastics are a definite no-no for use in the microwave; these contain potentially harmful chemicals that could leach into the food and also lack the internal integrity and will almost certainly melt.

Can You Microwave Tupperware?

tupperware containers

Tupperware is a type of plastic which has been used in the kitchen for many years. It can withstand extreme temperatures of between -25 to +160o C, and can be used straight from the freezer to the microwave without any ill effect.

You will need to exercise some caution here because even though tupperware has been used for many years and is considered safe to use, not all tupperware containers are microwave safe. You still need to look for the three wavy lines or the “microwave safe” message.

Plus even though tupperware containers are longer made using BPAs, they may have been replaced with BPS or BPF which is still not 100% safe to use. But whatever you decide, definitely don’t use any tupperware container in the microwave that doesn’t display the “microwave safe” message or the three wavy lines.

Can You Microwave Foil (aluminium foil)?

potatoes on aluminum foil

Aluminium foil is a great aid when cooking foods in the oven. However, it should never be used in a microwave. The problem is that aluminium foil is very thin, and it will heat up too fast in the microwave leading to it catching fire.

Added to which, if the foil is creased or crinkled, it can cause sparks that could damage the microwave or cause a fire. You should never put aluminium foil in a microwave under any circumstances.

That includes those aluminium foil trays that are used to cook foods in a conventional oven.

Can You Microwave Ceramics?

ceramic bowl and cups

You need to tread carefully when it comes to ceramic dishes and plates. Some ceramics are made using some sort of metal which could overheat and cause the container to crack or burst.

Then there are those decorative ceramic plates with metallic trim. These are a definite no-no as the metal could cause a fire.

The only ceramic ware that can be safely microwaved is ceramic ware that is microwave safe. Look for the three wavy line symbol or the words “microwave safe” before placing any ceramic ware in the microwave.

Can You Microwave Glass?

Pyrex glass measuring cup filled with cherries

Just like ceramics, glass has been used for years in the kitchen. Glass plates and dishes have been made for use in conventional ovens but this is a special type of glass. It’s known as borosilicate glass and has special heat bearing properties.

Often sold under the brand name of Pyrex, borosilicate glass is microwave safe. However, always check and ensure that it displays the three wavy line symbol or states “microwave safe” before using it in the microwave.

Regular glassware should not be used in the microwave as it is not resilient enough to withstand the high heat produced during microwave cooking. Regular glassware contains many little bubbles of air trapped inside the glass. These air bubbles can expand when heated up causing the glass to shatter.

Can You Microwave Paper Plates?

food on paper plate

It seems like everything that can be used in the microwave has conditions to use. Paper plates are no exception. As long as they are plain white paper plates and not printed or coloured paper plates, they should be fine to use in the microwave.

Printed or coloured paper plates could leach chemicals into the food and in some cases cause fires. If you intend to use paper plates in the microwave to cook particularly greasy foods, you might need to double or even treble the number of plates you use to prevent any grease leaking through the paper plate.

Can You Microwave Paper?

person decorating cookies on a baking tray with wax paper

It is generally safe to use wax paper, plain kitchen paper and plain paper bags in the microwave. That’s as long as they are not made from recycled paper and are not coloured.

Brown paper bags can catch fire in a microwave so they should never be used. Recycled paper can contain harmful chemicals which could leach into food.

Can You Microwave Cardboard?

The short answer is no, you should not microwave cardboard. This is because many cardboards contain glues and other chemicals that could leach into foods.

Some takeaway cardboard boxes even contain metal handles or fasteners which could cause fires.

Can You Microwave Metal?

You should never use metal containers in the microwave because metal surfaces reflect microwaves. This increases the risk of a fire breaking out in the microwave.

This includes all kinds of metal including aluminium foil.

Can You Microwave Insulated Travel Mugs?

Insulated travel mugs are often made using stainless steel parts which should never be put in a microwave. If your insulated travel mug has the three wavy line symbol or the words “microwave safe” then it’s OK to put it in the microwave.

If not, never put your insulated travel mug in the microwave. 

Can You Microwave Ziploc Bags?

person putting food in a ziploc bag

As long as it says “microwave safe” or displays the three wavy lines symbol, it’s safe to use Ziploc bags in the microwave. You will need to stick to the instructions on the packaging concerning the correct procedures and temperatures to microwave when using Ziploc bags, but as long as they are microwave safe it should be fine.

I’m talking about the official, genuine Ziploc bags here. If you have bought a cheaper alternative, made by an unknown company, and there’s no microwave safe wording or symbol, it would be unwise to use them in the microwave.

Can You Microwave Polystyrene?

This is another product that can be used in the microwave under certain conditions. The problem here is polystyrene has been linked to some types of cancer due to the compound styrene which is found in polystyrene.

Just like some plastics, when the polystyrene is subjected to the heat of the microwave, chemicals can leach into the foods causing a health risk.

However, there are certain polystyrene containers that have been specifically designed for microwave use. These shouldn’t cause you or your family any problems as long as they display that “microwave safe” message or carry the three wavy lines symbol.

But to be on the safe side, I recommend using a different type of container. One that there’s no doubt about its safety when microwaved. Like some of those on the list above.

Nothing

Microwave

The last item to make our non food list of items not to be microwaved is nothing. What I mean is it can seriously damage your microwave if you start it up with no food inside.

The thing is the microwaves produced need to go somewhere and need to be absorbed by something. Otherwise they travel around the microwave’s cavity and bounce off each other. This can lead to the microwave becoming damaged.

It could even catch fire or in extreme cases, explode. Not to mention the damage that could be done to the capacitor or the motor! Never turn the microwave on with nothing in it.

What Foods Should Never Be Microwaved?

microwave

Now that we’ve looked at all of the types of cooking containers you’re likely to use in your kitchen, let’s turn our attention to foods that should never be cooked in a microwave. They include;

Hot Chilli Peppers

If you subject hot chilli peppers to the heat of a microwave it evaporates the compound that makes them spicy. Once the microwave door is opened, those compounds attack your eyes and throat in the same way as pepper spray!

This is because the heat in the microwave is too much for the pepper to withstand. Using fresh hot chilli peppers is bad enough, but putting dried chillis in the microwave can cause them to catch fire.

Bell Peppers

bell peppers

It’s not just hot chilli peppers that shouldn’t be microwaved either, bell peppers are likely to catch fire if subjected to the radiated heat from a microwave as well.

Tomato Based Sauces

There are no health concerns connected with putting tomato based sauces in a microwave to reheat. The problem is these sauces are likely to splatter all around the microwave and create a large mess.

If you decide to reheat a tomato sauce in the microwave you should do it in a container with a vented lid or learn how to clean a microwave.

Grapes

Grapes or any whole fruits that have a high water content and a thin skin can explode if subjected to the high heat of a microwave. Plus the skin of the grape will scald and blister and the whole thing will be an unpalatable mess. Added to which the vitamin content will be lost as well.

Blueberries

Just like grapes, blueberries are likely to suffer a similar fate if microwaved. The high heat will cause the inside to heat up rapidly causing the skin to burst.

Whole Apples

apples

It can be tempting to make the equivalent of baked apples in the microwave. However, don’t do it. Not only will the apples lose their vitamin content, they are also likely to explode under the extreme heat found in the microwave. 

Any remaining fruit is likely to have a bad, burnt taste as well.

Frozen Berries

Just like grapes and blueberries, frozen berries run the risk of exploding all over the interior of the microwave. Plus there’s also a good chance that they’ll lose all of their antioxidant properties if subjected to microwave cooking.

Whole Eggs

Eggs

I’m talking about eggs in their shells here, not scrambled eggs which come out pretty well if cooked in a microwave. If you’re tempted to make a boiled egg or a hard boiled egg in the microwave to save time, don’t do it.

The inside of the egg will heat up to such an extreme level that steam will be created which, because of the shell, has nowhere to escape. This leads to the egg exploding and creating a mess inside the microwave.

Carrots

Believe it or not, the mineral content found in carrots could cause the microwave to catch fire. Carrots contain iron, magnesium and selenium which are all metals and can produce sparks if microwaved leading to fire. 

Processed Meats

Processed meats like hams, bacon or meats found on the deli counter are considered safe to microwave. However, they do contain chemicals and preservatives to extend their life.

When those chemicals are exposed to high heat from microwave radiation, those chemicals can have an adverse effect on human health.

Breast Milk

Heating breast milk that has been expressed and stored in a fridge could cause risks to your baby. This is because it may heat unevenly and could scald your child.

Dry Leafy Greens

It’s generally OK to cook leafy greens in the microwave as long as they are wet. If they’re dry, they could catch fire. This is because leafy greens need moisture to cook. If not, they dry out too rapidly which could cause them to catch fire.

Cooking Oils

Due to the way microwaves work, it is not a good idea to heat cooking oils in the microwave. Firstly it’s the container that gets heated first and not the oil.

Then once the oil does heat, it loses many of its properties. There’s greater oxidation and a loss of phenolic content. This leads to the oil tasting “off” (this is especially true for extra virgin olive oil).

Frozen Meats

We’ve all done it at some point, we forget to get the meat out of the freezer and need it for dinner right away. But before you stick it in the microwave, you should know that this is potentially dangerous.

Why? Because some of the meat will start to cook whilst others parts will remain frozen.  This can lead to the growth of harmful bacteria that could cause food poisoning or other complications.

Bread

Bread

Reheating bread in the microwave won’t cause you any physical harm. However it might put you off bread for life. The starch in the flour melts during the microwave process which leads to the bread becoming a chewy hard mess.

If you want to reheat bread to restore its crunchy crust, use a conventional oven and not the microwave.

A Cup Of Water For Making Tea

The problem here is that the temperature of the water affects the flavour of the particular tea being made. For instance green tea and white tea need a water temperature of 76 to 82o C(170 to 180o F), herbal teas should be brewed using water at 98o C (210 F), whilst black tea should be brewed with water at a temperature of at least 93o C (200 F) or more.

The problem here is that there’s no way to tell the exact temperature of microwaved water. Whereas an electric kettle is designed to heat water to around 100o C (212 F).

This could result in your particular tea not tasting as nice as it should if you rely on the microwave to heat the water for you.

Previously Microwaved Foods

If you’re thinking of reheating foods that have already been reheated in the microwave once before, don’t do it. Reheating food in the microwave for the second time increases the risks of bacteria breeding in the food to an extent that could make you ill.

Similarly leftover food that’s been stored in the fridge should be consumed within 48 hours and if you have thawed out some frozen leftovers they should be eaten within 24 hours.

You need to ensure that the food is piping hot before eating to reduce the risk of illness due to bacterial contamination.

SEE ALSO: Can You Put Microwave Meals/Ready Meals/TV Dinners In An Air Fryer?

Frequently Asked Questions

Why can’t I put aluminium foil in a microwave?

You can’t put aluminium foil in a microwave because aluminium is a metal which will heat up extremely fast and could catch fire. Plus if the foil is creased or wrinkled, it can produce sparks which can lead to fires.

Why can’t I put carrots in the microwave?

You can’t put carrots in a microwave because they could catch fire. This is due to the high mineral content in carrots which includes iron, selenium and magnesium which are all metals and could cause sparks to fly and catch fire.

Can paper plates go in the microwave?

Paper plates can go in the microwave as long as they are microwave safe and carry the three wavy line symbol. Avoid paper plates with patterns or coloured paper plates. Plain white paper plates should be OK but it’s always best to check the packaging before use.

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