Marshmallow in the Microwave Experiment

This tasty edible science experiment explores what happens when you heat marshmallows. Your kids will love this delicious marshmallow in the microwave experiment.

Microwave Marshmallow Experiment 50 Seconds

Have you ever heated a marshmallow in the microwave? It’s super fun to watch the marshmallow expand and blow up more than double the size. 

This marshmallow science experiment is a great sensory activity for kids since they need to use different senses to examine what happens after a marshmallow has been heated for a certain time. 

And because of its sugary goodness, the microwave marshmallow experiment has become the favorite science experiment in my kids’ books!

The Microwave Marshmallow Experiment



  1. Decorate your marshmallows with food coloring or icing gel. We used a clean paintbrush and dipped it in red Wilton icing gel and wrote on the marshmallows how long we are going to heat them in the microwave. Not super pretty, but having the numbers on the marshmallows makes it easier to keep track when you look back at the pictures. Microwave Marshmallow Experiment Seconds
  2. Place one marshmallow on a plate and microwave it for 10 seconds.
  3. Remove the marshmallow from the microwave and place an uncooked marshmallow next to it for comparison.
  4. Use any eating utensils to make a hole in the marshmallow and see what happens to the inside.
  5. Make observations: How does it look? How does it feel? How does it taste? What happens after you wait for it to cool down? 
  6. Repeat steps #2-5 but with longer times in the microwave. We added 20 seconds each time we heated the microwave, so 30, 50, 70, and 90 seconds. 

Isn’t it mesmerizing to watch the marshmallow grow and expand in the microwave? My kids and I can do this all day!

This experiment is also an excellent opportunity to practice critical thinking. After seeing what happened with the marshmallow after 10 seconds in the microwave, ask your child to make an educated guess about what will happen to the marshmallow after 30 seconds. Your child should be able to make a prediction before you heat the marshmallows about the size, color, taste, and even texture of the marshmallows.

Here are our observations – your results might be different depending on your microwave.

After 10 Seconds

The marshmallow grew bigger in size. The entire marshmallow was gooey and melted in our mouths. 

Microwave Marshmallow Experiment 10 Seconds

Microwave Marshmallow Experiment 10 Seconds Melted

After 30 Seconds

The marshmallow increased in size even more than the previous marshmallow. A small hole had formed at the bottom of the marshmallow. The marshmallow dried and flattened as it cooled. 

The marshmallow was extremely sticky when we tried to lift the top to look inside. There was a big hole in the middle. As the marshmallow continued to cool, it got even drier and stickier and stuck to our teeth when we tried to chew it.

Microwave Marshmallow Experiment 30 Seconds
Microwave Marshmallow Experiment 30 Seconds Inside

After 50 Seconds

The marshmallow continued to get bigger as we microwaved it longer. The bottom of the marshmallow started to brown. Even before it cooled down the marshmallow had dried on the outside. 

We enjoyed eating the outside of the marshmallow because it was crunchy. However, parts of the inside and the bottom were burnt and bitter to eat. Also, the bottom was too sticky and hard to even remove from the plate.

Microwave Marshmallow Experiment 50 Seconds
Microwave Marshmallow Experiment 50 Seconds Inside

After 70 Seconds

Yup, you guessed it – the marshmallow got even bigger! The marshmallow actually was not too different from the 50 seconds one, but the bottom did get more burnt. Hence, the color got darker and was not pleasant to eat. 

My kids tried to remove the bottom of the marshmallow from the plate and ended up breaking it into pieces.

Microwave Marshmallow Experiment 70 Seconds
Microwave Marshmallow Experiment 70 Seconds Inside

After 90 Seconds

I was a little afraid of heating the marshmallow for that long because I wasn’t sure if it would explode. 

Since we used the microwave so much, the turntable was still warm when we placed this one in the microwave. Therefore, you could see that the bottom started to melt even before I started the microwave. And as a result, when the marshmallow expanded, it tipped over.

We didn’t even try eating this marshmallow because it was pretty brown throughout. It would have been really bitter. You can see how thin the outer layer got since it expanded so much. 

Microwave Marshmallow Experiment 90 Seconds
Microwave Marshmallow Experiment 90 Seconds Inside

We stopped after 90 seconds because the marshmallow was quite burnt already. If we continue to increase the time, we will just get a super dry and brown marshmallow. I didn’t want the burnt smell in my house!

Science Behind the Microwave Marshmallow Experiment

Marshmallows consist of tiny air bubbles surrounded by thing walls of gelatin and sugar syrup. 

The water in the sugar syrup heats up and evaporates. The gas fills the air bubbles in the marshmallow, causing them to expand. Consequently, the marshmallow puffs up.

As the temperature increases inside the marshmallow, the sugar caramelizes and turns brown. This is due to the Millard reaction, which we explored with the secret messages on marshmallows experiment.

Microwaving the marshmallows also causes the gelatin to melt. The gelatin is what helps marshmallows keep their shape. Therefore, as the heated marshmallow cools down and steam dissipates, the marshmallow collapses. Since there is less water in the marshmallow, the marshmallow becomes dry and crunchy.  

Final Thoughts on the Marshmallow in the Microwave Experiment

Which marshmallow did you prefer to eat? I actually liked the 30 seconds one because the outside just started to become crunchy and the inside was still gooey. My kids actually preferred the 50 seconds one since it was crunchier, but the inside was too bitter for me.

I hope you and your kids enjoyed this experiment. If you want to see more stuff grow in the microwave, try the ivory soap experiment! 

For more candy science, check out:

Marshmallow in the Microwave Experiment Pin

1 thought on “Marshmallow in the Microwave Experiment”

  1. Thanks Betty, we did this today with our grandsons ages 5 & 6. They absolutely loved it. Thanks for another great experiment!


Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top