Ever noticed that certain veggies spark when cooked in the microwave? Whether you have or not, it will be interesting to find out why this happens with help from our friends at NPR.

Once equipped with this fun knowledge, observe what happens when heating up some of your Thanksgiving leftovers!

Minerals and Metal

Dense vegetables such as green beans, carrots, spinach, and green peppers contain a higher amount of minerals in them than other types of food. These minerals - which include iron, magnesium, and selenium – act like tiny pieces of metal and create what is known as an “arcing effect” in microwaves.

An arcing effect is when sparks occur as a result of electromagnetic waves in a microwave reflecting or bouncing off metal. On the plus side, the arcing doesn’t cause any damage to the food. But the bummer is that it does prevent food from being thoroughly heated through.

Certain Electric Fields Are Needed

It turns out that just having metal present isn’t enough to create an arcing effect though. Microwaves work by sending out electromagnetic waves that vibrate the water, fat, and sugar molecules in food, creating heat. The microwave generates an electric field, but the intensity of the electricity varies throughout the microwave.

If a small piece of metal is present in the microwave, it can locally enhance the electric field and make it stronger than the air surrounding it. For example, when you cut a carrot into small pieces and heat them in the electric field, the pieces will develop different individual charges. Sometimes these charges will cause sparks between the pieces - similar to a static charge when you touch your doorknob.

This means that a lot of metal isn’t needed, just a difference in the electric properties from one spot to another – say, from a piece of a green bean with metal to one without any metal. Chopping vegetables into small pieces and heating them close together increases the likelihood of sparks.

On the other hand, if you reheat a vegetable in pasta sauce, a spark will not be likely to occur. This is because the specific electric field needed will not be created due to the presence of the sauce.

Shape Also Plays a Role

It has been found that shape also helps sparks to form - especially pointy edges. So vegetables or plants that have edges or points, like Brussels sprouts or green beans, can act to enhance the electric effect.

Don’t forget to check out whether your Thanksgiving leftovers will create an “arc effect”! To increase the odds of your veggies sparking, perhaps you should (innocently) request green beans, sautéed carrot slices, or Brussels sprouts to go with your Thanksgiving dinner…

Looking for more Never Stop Asking "Why?" questions? Catch up on all of the past "Why's" on the blog!