Is it safe to microwave food in cardboard?

I imagine this question comes from a place where you are either a college student living your life out of a dorm with limited space (and money) to buy all the necessary kitchen essentials. Or are you one who prefers living in the “Age of convenience”?

I’ve been there too myself, many a time before when thoughts of trying to reheat pizza or Chinese food in the box rather than transferring to a ceramic plate came to my mind.  Call me lazy or whatever, but the thought of microwaving food in the cardboard boxes they came in always seemed so convenient. No mess and no washing dishes afterward seemed like the perfect situation any anyone youngster could hope for.

But in the confined spaces of my dorm, I obviously didn’t want to start a fire, so I did my research and found some solid science-backed reasonings on whether it’s safe to microwave food in cardboard containers.

This article will teach you whether or not it is safe to microwave food in a cardboard container. You will learn about the facts, tips, and alternatives.

Is it safe to microwave food in cardboard?

It depends…

Microwaving food in cardboard containers is a very grey area. Without taking the appropriate precautions, it can be easy to start a fire, make the cardboard collapse, leach glue onto your food, etc.

But if you use containers that are specifically created for use in the microwave or use the appropriate temperatures and cooking time then yes, it can be safe.

Still confused? Keep reading as I delve further into all things cardboard.

Can cardboard go in the microwave?

Before I can answer this question, you need to understand how a microwave actually heats up food (or anything placed inside it).

A microwave will usually work by agitating the water molecules in food by hitting them with microwave rays which in turn heats the water and turns it into steam.

This is why when you heat food for longer you might have noticed that it starts to dry out because it’s losing out all that water content to evaporation.

Now consider placing the cardboard in the microwave and heating it as well. Most cardboard, like paper, is made from wood pulp and has a moisture content of 9-12%. Heat that up and its moisture content will start to radically decrease, depending on how high the temperature was and how long it was heated.

When the water content drops to around 1%, the cardboard is sufficiently dry enough to catch fire.

So to answer your question, NO, cardboard cannot go in the microwave. At least definitely not an empty cardboard container without the hazards of starting a fire.

Can cardboard containers with food & drink be microwaved?

Now, this is where you have entered the grey zone.

In some situations, cardboard containers can be used to reheat food in the microwave. But it should only be used under constant supervision, for reheating food for a minimum time, and shouldn’t be done repeatedly.

Cardboard containers (like the ones for instant Ramen noodles) should definitely not be used for long-term cooking your food in the microwave.

Therefore, it should be safe to only reheat your food in the cardboard container in the microwave.

But again, there are still exceptions! Not all cardboard packaging is created alike. Some are held together with glue, some are printed with ink and some may even have inner linings of plastic or wax. Never use these types of cardboard packaging in the microwave.

Which cardboard packaging shouldn’t be microwaved?

Feeling more confused than ever? Well, it is a tricky business this microwaving cardboard after all. I’m going to keep it simple:

  • Some cardboard may contain tiny pieces of metal, which can create sparks when put into the microwave and damage your microwave along with potentially starting a fire.
  • Some cardboard containers might be held together with glue, heating them in the microwave might cause the glue to melt and mix in with your food, or the glue can even emit toxic fumes when heated.
  • Some cardboard containers (actually most cardboard containers) are printed with their brand’s logo and name. Unless otherwise mentioned, these inks may not be safe and melt onto food when they come in contact with it.
  • Cardboard containers can sometimes be lined with a plastic or wax layer. When heated this layer can melt off onto your food. However, the good thing is, that this kind of cardboard packaging is easy to identify. The surface usually is smooth and glossy, unlike typical cardboard which is rough.

My takeaway from all this is if you are unable to identify whether your cardboard may or may not contain any of the above, it would be better to switch to a more microwave-friendly container like glass.

How to microwave cardboard safely?

While this is not something I would recommend but if you find yourself stuck in a pinch then follow these tips to microwave cardboard as safely as possible.

  • Always heat the cardboard for as short a period of time as possible and that too in small intervals.
  • Place the cardboard on a plate or in a bowl to catch any sparks or flames.
  • Always keep an eye on the microwave while you are microwaving cardboard in case of a fire.

Tips to Microwave Cardboard Safely:

Follow these additional safety tips if you do decide to microwave cardboard containers.

Read package labels carefully: Most of the time manufacturers will print guidelines on whether their products are safe to be used in the microwave.  Always check for a small three-wave icon which means the product is microwave safe. Read instructions carefully before starting and follow them precisely.

Check for Metal: Before microwaving cardboard containers, check if they have any metal objects on them such as handles, staples, or foil. These can cause a spark which may lead to a fire when heated in the microwave.

Keep a close eye: Never leave the microwave unattended while it is running with a cardboard container. If you see any smoke rising, immediately, turn the microwave off and remove the cardboard from it and douse it with water or a flame extinguisher if necessary.

Use the appropriate temperature: Never set the microwave temperature too high while microwaving cardboard, doing so may dry out the cardboard and increase your chances of starting the fire.

Check the chemical composition of the cardboard: Any cardboard container like cups, boxes, and bowls containing plastic layers, wax coating, or those with styrofoam insulation should not be kept in the microwave because they can release dangerous fumes or melt, and mix harmful chemicals with your food.

Avoid heating liquid foods: Avoid heating foods with high water content, like soups or coffee and tea. Heated liquid can cause the cardboard to get soggy and potentially break down.

Takeaway

With the rise of the eco-conscious movement, more and more companies are resorting to using cardboard packaging instead of plastic ones.

And I mean, why not? It’s biodegradable and better for our planet, after all. But just because it’s good for the planet doesn’t mean it is good for the microwave.

While microwaves are going to be our trusty sidekick in this age of convenience, this doesn’t mean that anything can just be tossed into it for microwaving without following the proper precautions.

Make a practice of inspecting the cardboard box before putting your meal in the microwave to avoid any potential health or fire risks.

The outside of the box will probably be labeled with instructions as well. If it has the three-wave symbol, it means it will be safe to use in the microwave.

If at all uncertain, reheating your food in a microwave-safe container is a much better and safer option.

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