You have a pizza in a cardboard box and you need to reheat it before eating. Now, you may be wondering if it’s safe to put cardboard in the microwave. After all, you don’t want to set your kitchen on fire!
Can cardboard go in the microwave? Yes, cardboard is microwave safe in most cases. In only a few instances, it is not allowed in the microwave oven. Cardboards with any kind of metal, wax paper, etc. are usually not allowed to go in the microwave.
Let’s explore how cardboard interacts with microwaves and whether or not it’s safe to microwave food in cardboard containers. Also, I’ll share some tips on how to properly microwave cardboard so that you can avoid any dangerous accidents.
Interaction of Cardboard With Microwaves
The use of cardboard is vast in the food industry. In particular, fast foods like pizzas, burgers, and other dry to semi-dry foods come in cardboard, more often when it is a take-out or parcel.
The moisture content of cardboard is usually between 9 and 12 percent (5). If you put it in the microwave, the moisture content will start to diminish, and depending on how long it spends in the microwave and how large its surface area is, it might drop to 1%.
This process can happen quickly, and if you keep the microwave on, the cardboard will likely become fully dry and catch fire. It is worth noting that this situation only applies when you put cardboard in the microwave by itself, with no other items in the microwave (such as food or drink).
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How Does the Microwave Heat Cardboard?
The microwaves heat up the water molecules present inside the food as well as the cardboard. Cardboard is made of cellulose fibers, which are basically long chains of sugar molecules (glucose).
These sugar molecules have a dipole moment. This means that they can rotate in the presence of an external electric field, such as microwaves.
The rotation of these molecules creates friction and heat, which is then transferred to the surrounding molecules, thus heating up the cardboard.
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Safety of Cardboard in Microwave
While it is normally safe to use cardboard in the microwave, it is always a good idea to read the manufacturer’s instructions before doing so.
In order to heat food in a microwave, the water content of the food or liquid being heated is used to generate heat. When you microwave something, it forces the water molecules in the food to vibrate faster and faster, creating friction and heat that cooks it.
Due to the lack of moisture in cardboard, there aren’t as many molecules to move around, so it doesn’t get as hot as your food. In most cases, this makes it safe to microwave cardboard. There are, of course, exceptions to this rule.
Reheating instructions are sometimes plainly stated straight on the container and package when you order a takeaway meal or pizza. If the box is not labeled as microwave safe, do not use it in the microwave.
When microwaving cardboard, make sure you only heat it for a few minutes at a time. Although using microwave-approved cardboard is safe and unlikely to catch fire, it is best to keep the cooking time to a minimum.
Otherwise, the moisture content of the cardboard may drop, perhaps causing a fire. If you follow proper procedures, you should be able to nuke microwave-friendly cardboard with no problems.
It is also not safe to use cardboard boxes or packages that contain any kind of metal, foil, wax paper, etc. in them. This may cause a spark in the microwave and a meltdown of the wax paper, leaking into the food.
However, it is always better to transfer the food from the cardboard container to a microwave-safe dish before microwaving, if you are not sure about the particular cardboard.
Will Cardboard Light on Fire in the Microwave?
Paper and cardboard come to mind when we think about starting fires and materials to use to do so because they spark up rapidly and burn easily. The flammability of cardboard is what might be making you think about if cardboard can be put in the microwave.
If the cardboard is heated for too long in the microwave, then it may catch fire, though the chances are low. This happens because when the cardboard is heated, its moisture level keeps reducing, eventually making it dry and prone to catching fire.
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Though most cardboards are generally safe to go in microwave ovens, not all types of cardboard can go in the microwave.
Usually, only the cardboard types that are plain and do not have any kind of wax or plastic lining, foil inside or outside, ink, glue, or any other kind of coating can be microwaved.
Cardboards that have a shiny metallic surface on either side should not be microwaved as they can cause sparks and fires. If you are unsure about the type of cardboard, it is always better to play it safe and not microwave it.
LEARN MORE: Can You Use Wax Paper in the Microwave?
How Long Can Cardboard Be Microwaved?
When microwaving cardboard, make sure to heat it only for a few minutes at a time. Cardboards should not be microwaved for long periods of time. You can microwave it for a shorter period of time, such as 60 to 120 seconds.
If you wish to microwave cardboard for a longer period of time, break it up into 30 second or 1-minute intervals before continuing the heating process.
However, you should not go more than 120 seconds in a single session. Although foods can be heated more quickly when nuked on a cardboard surface, coffee and tea may not. It may take longer for cardboard beverage containers to heat up.
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Can You Cook in Cardboard in Microwave?
Cooking food in cardboard is not advised as it can be dangerous. While it is okay to reheat food in cardboard containers, cooking should be avoided.
The reason behind this is that when you cook food, the water content in the food starts boiling and evaporating. If there is no water content left, then the cardboard can catch fire.
Hence, it is always better to cook food in microwave-safe containers and then transfer the food to cardboard containers after cooking, if needed.
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Tips on Microwaving Cardboard
Here are some tips that you can follow when microwaving cardboard:
- Use plain cardboard that does not have any kind of coating or plastic lining.
- Do not microwave cardboard for more than a couple of minutes at a time.
- Avoid cooking food in cardboard containers.
- Before you microwave the cardboard, remove any paper, plastic, or metal fragments. Remove the plastic lid from disposable coffee cups, the plastic pizza box holder, or the metal clip that secures the lid before microwaving it, for example.
- Do not use wax paper, aluminum foil, or any other kind of metal in the microwave.
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So, you must have got your answer by now. If your pizza takeaway box has no wax, plastic lining, or any kind of foil, you can easily reheat your pizza in the microwave.
And the bottom line is that plain cardboard can be microwaved, and it should only be done for a short period of time. It is not advised to cook food in cardboard containers in the microwave.
If you follow these tips, then you should be able to safely reheat food in cardboard containers in the microwave.