What happens if you microwave marshmallows?

Can you make s’mores indoors? And can you turn this into a science experiment, and create something that is both delicious, and educational? Challenge accepted!

what happens if you microwave marshmallows

We love camping. When we go camping, finding a few good marshmallow sticks is one of the first things my kids do when we arrive. Most of our family like to slow roast their marshmallows over hot coals, so that the marshmallows become all soft and golden. I’m more impatient, so I tend to go for flame-grilled charcoal-coated version. But either way, we all agree that roasting marshmallows over an open fire is the best.thing.about.camping.

But then we borrowed a book from the library called Kitchen Science Lab for Kids: Edible Edition by Liz Lee Heinke, and that.changed.everything.

We discovered the possibility of microwaving marshmallows. How had we not thought of this before???

Of course, we had to turn this idea into a little edible science experiment (because that’s what we do in our house, mostly as a way to justify eating sweets). We thought we would test: 1) different types of marshmallows to see which ones work best; and then 2) different amounts of time in the microwave to see what difference this makes.

Suitable for

I’m pretty sure any age group would like to try eating these tasty microwaved marshmallows! But as a science experiment I’d say this is most suitable for primary (elementary) school aged kids. Jewel was 11 years old and Bumble Bee was 8 years old when we first did this in our house. (Although we’ve replicated the experiment a few times since!)

Younger kids can learn about how microwaves work (see below). Older kids can focus on following the scientific method in their experiment, and see if they can come up with a way to accurately measure the expansion / inflation of the marshmallows.

How do microwave ovens work?

Microwave ovens use microwaves to cook food. Microwaves are waves of electrical and magnetic energy that move together through space. The microwaves are produced by an electron tube called a magnetron. When you start cooking, the magnetron takes electricity from the power outlet and converts it into high-powered microwaves. These microwaves are then reflected within the metal interior of the oven, where they are absorbed by food. Microwaves cause the tiny water molecules in food to vibrate. Vibrating molecules produce heat, and so as the water molecules vibrate more, the food is cooked.

Microwaves have three characteristics that allow them to be used in cooking:

  1. They are reflected by metal (and so can be reflected inside the metal interior of the oven).
  2. They pass through glass, ceramics, some plastics, and similar materials (which is why you can safely put your food on microwave-safe plates to cook).
  3. They are absorbed by food (which is how they cook the food).

(Please note: Whilst microwaves don’t heat up plates directly, they can still become hot because the food on the plate becomes hot, and this heat is then transferred to the plate.)

Marshmallow experiment part 1: What type of marshmallows work best?

We tried out three different types of marshmallows that are readily available in our local grocery stores:

  • The So Soft Marshmallow Co. Jumbo Roasters (large size, white)
  • Pascall Marshmallows (medium size, pink & white)
  • The So Soft Marshmallow Co. Minis (small size, colourful)

We also use chocolate coated digestive biscuits to make our s’mores, as we don’t have Graham Crackers in Australia, and these are the next best thing.

Of course, being a science-loving family, we had to follow the scientific method in our investigations.

Step 1 – Ask a question: What happens if you put marshmallows in the microwave?

Step 2 – Form a hypothesis: Marshmallows will inflate (expand / puff up) in the microwave. The different types of marshmallow will react similarly.

Step 3Experiment: We put the three different types of marshmallows on a plate, and put them all in the microwave at the same time, to see what would happen!

Here’s the ‘raw’ marshmallows ready to go in

And here they are after being in the microwave for 30 seconds.

different types of marshmallows coming out of the microwave

Step 4Observe and record: The different types of marshmallows didn’t react the same at all! The mini ones expanded slightly, but became quite firm. The medium sized pink and white ones didn’t inflate, but more melted. The large Jumbo Roaster ones expanded quite a lot and became all fluffy! We did this a few times and were able to replicate these results.

Step 5Draw conclusions: Different types of marshmallows don’t necessarily react the same when microwaved. Some types of marshmallows expand / inflate / puff up, and some don’t.

Step 6Share your findings: That’s what this blog is all about. 🙂

Why do some marshmallows inflate in the microwave, but others don’t?

Marshmallows are mostly made of tiny air bubbles that are encased in sugar, gelatin and water. When you cook marshmallows in your microwave oven, the microwaves make the water molecules vibrate very quickly, which warms the air inside the marshmallows and causes it to expand. My hypothesis is that the larger marshmallows have a stronger and stretchier sugar & gelatin “wall”. As the air inside expands, it pushes against this “wall” and causes the marshmallow to inflate. I’m not sure why this doesn’t happen with the other marshmallows – perhaps their sugar and gelatin make-up means that the hot air can escape, and so they don’t inflate.

We then went on to the next part of our experiment

Marshmallow experiment part 2: How long should you microwave the big marshmallows for?

This time we zeroed in on the Jumbo roaster large marshmallows, as these were the ones that reacted best in the first part of the experiment. We wanted to see how the length of time that the marshmallows spend in the microwave affects the results.

Step 1 – Ask a question: How does the length of time that the marshmallows spend in the microwave effect how much they inflate?

Step 2 – Form a hypothesis: The longer the marshmallows spend in the microwave, the more they will puff up.

Step 3Experiment: We tried comparing different lengths of microwave time, by microwaving the first marshmallow, and then quickly stopping the microwave so that we could put a second ‘raw’ marshmallow on the plate, and then microwaving them both, so that way we could directly compare two marshmallows side by side that had been microwaved for different lengths of time.

Note: we might have used up (i.e. eaten) a fair few deliciously gooey marshmallows after each photos were taken – the ‘no eating in the lab‘ rule doesn’t count when the lab is your kitchen!

marshmallows after being microwaved - none, 30 seconds and 1 minute

Inside the microwave

inside the microwave

1.5 minutes, vs 1 minute, vs none.

normal vs microwaved marshmallows

After 2 minutes in the microwave – look how big it’s gotten! It’s almost as big as Jewel’s head! (Well, not quite…)

after 2 minutes - look how big it's gotten!

Over-cooking causes the inside to caramelize (which can also be tasty, but in a crunchy, instead of gooey, way)

over-cooking causes the inside to caramalize

Step 4Observe and record: We discovered that extra time in the microwave increased the puffiness (or the amount of inflation) up to a certain point. For us, that point was about 90 seconds. After that the marshmallow stops inflating and instead the inside starts to caramelize. You can smell the caramel smell when this starts to happen. The texture of the marshmallow changes a lot when this happens, and instead of being gooey, it becomes hard and brittle.

Step 5Draw conclusions: If you want to make homemade s’mores using the microwave, then you need to microwave your marshmallows only to the point where they are still soft and goey, so that they can be squished between two halves of a coated biscuit for ultimate indoor s’mores deliciousness.

Note: these microwaved s’mores won’t taste the same as the campfire variety – they don’t have the smokiness, and the marshmallow is much more stretchy. But they are still awesome!

microwave marshmallow smores

Bumble Bee gives them the thumbs up!

Girl eating microwave marshmallow smores

Step 6Share your findings: We’ll view these new indoor / microwave s’mores as an addition to, instead of a replacement of, our usual outdoor camping ‘smores. But they are definitely easier to do at home!

what happens if you microwave marshmallows and can you make smores indoors

If you try this too, whether you love or hate them, please let us know in a comment below!

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