How Does a Microwave Reheat Food and Is It Safe?

You may or may not already know that a microwave oven uses radiation to heat food or liquids. This article is not about how a microwave works in terms of internal engineering. Instead, we are here to talk about what happens to your food to make it heat up.

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Furthermore, more and more people are concerned with whether it is even safe to heat food in a microwave, going so far as to ban them from the house entirely. So, what’s happening in there?

How Does a Microwave Reheat Food?

How Does a Microwave Reheat Food

The answer to this question actually relates both to how a microwave works and to concerns about uneven heating in a microwave. You see, when the microwave generates heat through electromagnetic radiation, it is passing heat through the food or liquid inside.

When it performs this task, radiation excites the water molecules inside the food, causing them to crash into one another and generate heat inside the food. It also passes radiation through the microwave in “waves” or columns. Hence the name.

Unevenly Heated Food

For this reason, some parts of the food will be warmer than others, as some parts of the food will hold more water than others. That’s why when you first take the food out of the microwave, you may notice some parts of your rice, pasta, or pizza are still cold.

Microwave designers know of this sad, uneven reality, of course, so they created the spinning plate inside the microwave to ensure the food rotates while it is heating, ideally accessing. Still, your food may still end up unevenly cooked, overcooked in one spot and undercooked in another, especially when reheating food versus liquids.

Liquids are much easier to heat, and honestly the best thing to reheat in a microwave as it is, by definition, full of those water molecules that get excited. Thus, the best food to reheat in microwave is any kind of soup.

The Plate Is Not Hot!

You will also notice that when you are heating up a rice, pasta, or other dish that only takes a minute or two to reheat, the dish may remain cool or even cold.


Well, for the same reason microwaves heat liquids so well, they do not heat glass and plastic so well. Note that glass, ceramic, plastic, and other microwave-safe dishes do not have water molecules. As a result, they will take much longer to get piping hot than the food that is on or in them.

In fact, much of the heat you feel from a dish in the microwave is due to heat transference. The warm food is essentially heating up the dish.

Hacks for Reheating Food in the Microwave

Hacks for Reheating Food in the Microwave

To help you reheat your food effectively in the microwave and work with the technology as it is, you can employ a few hacks.

  • Add a damp paper towel or two. When you add a damp paper towel to your dish, either under or over your food, you are directing the radiation to the moisture in the paper towel and thereby preserving the moisture in your food, so plenty of water molecules are getting excited without your food drying out.
  • Move the dish to the edge of the plate. By moving your dish to the edge of the spinning plate inside the microwave rather than the center, you are subjecting it to more columns of radiating heat waves, allowing more of those waves to pass through your food and excite more of the water molecules within.
  • Cook in shorter increments. To be sure you don’t overheat your leftovers, you should stop the microwave every 30 seconds or minute to stir and check the food. Remember, you are looking for a way to evenly cook in an appliance notorious for uneven heating.
  • Add broth or water. Back to those water molecules. If you have a food that can stand a little more moisture, consider adding water, or even better broth, to the dish to generate more excited water molecules for more thorough heating.

Wait. Is It Safe to Use a Microwave?

Okay, so this question is a really important one to address as there is a ton of misinformation and hysteria on the internet about radiation generated by microwaves causing cancer or harming pregnant women.

The radiation energy that a microwave uses stays inside of the microwave while the microwave is in use unless you have a broken or faulty microwave that heats with the door open. In all but extreme cases, a microwave in good condition will not lead to radiation, which means you cannot be exposed to it.

Furthermore, in the event you had a microwave that somehow was damaged and is leaking radiation, it would be in such small amounts as to be insignificant to human health.

You can find statements attesting to this truth on trustworthy sites like the World Health Organization.

Food that has been heated through radiation waves does not retain any radiation that makes it dangerous. Thus, heating or reheating food in a microwave does not make it dangerous or more liable to cause cancer.

In terms of health, some nutritionists have warned that you may lose nutritional value from microwaving food, but that is only because some foods lose nutritional value when cooked, so it is not the microwave but the heating process in general that might make some foods less healthful.

In the end, it is perfectly safe to reheat your food using a microwave in good condition as it was intended to be used. Put the food inside, close the door, and warm up the food.

What do you think? Have you investigated the benefits or details of reheating leftovers in a microwave? What have you found? Let me know in the comments. I love to hear from my readers!

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