Write Secret Messages on Marshmallows with Invisible Ink

Learn how to write secret messages on marshmallows with invisible ink. This super cool secret ink trick will blow your kid’s mind!

Marshmallow Secret Message I _3 Mom

Can you guess what is the most widely practiced chemical reaction in the world? According to chemistry Nobel Prize winner Jean-Marie Lehn, the trophy goes to the Maillard reaction.

Think about the golden crust on freshly baked bread. Or the rich, nutty, toasted flavor of chocolate chip cookies. If you are not a fan of carbs, then think of the perfect steak with grill marks on the outside. Hungry yet? You can thank all of this deliciousness to the Maillard reaction.

One easy and yummy way to demonstrate the Maillard reaction to kids is through toasting marshmallows! And we are not just going to toast them until they are nice and crusty – we are going to write secret messages on the marshmallows with invisible ink!

How to Write Hidden Messages on Marshmallows



  1. Pour about 1/4 cup of water in a small container.
  2. Add about a tablespoon of baking soda to the water.
  3. Stir with the paintbrush or Q-tip.
    Marshmallow Secret Message Baking Soda
  4. Using the paintbrush or Q-tip, write the secret message on the marshmallows. It will be invisible (or at least very difficult to see)! I recommend writing just one character per marshmallow to ensure that the message is clear.
  5. Place a piece of parchment paper on a baking tray and put the marshmallows carefully on the parchment paper, message side up.
  6. Toast your marshmallows in the oven by placing your tray on the top rack and turning the temperature to broil. 
  7. Monitor your marshmallows closely because they may brown in less than a minute. Note: In the video below, I used the toast function and placed the tray on the bottom rack so that I can record the browning taking place. It worked as well, but it took a few minutes for the message to appear.
  8. Remove the marshmallows from the oven.
    Marshmallow Secret Message HELLO
  9. Wait until the marshmallows cooled completely before touching or tasting them! 

One thing my kids noticed was that the marshmallows increased in size when they were toasted. But then after we took them out of the oven, they quickly shrunk. They also observed that the texture of the marshmallows became crunchy after toasting.

The Science Behind the Invisible Ink on Marshmallows

As mentioned above, the chemical process called the Maillard reaction is behind why the marshmallow turns brown when toasted. 

When we heat our food, the reactive carbonyl group of the sugars reacts with the amino group of the protein. As a result, a multitude of new molecules are formed with a new flavor, aroma, and color. 

Even though food can turn brown for other reasons (for example, an apple turning brown due to oxidation), the Maillard reaction is responsible for the browning of food during cooking and baking.

But why would the baking soda and water solution brown faster than the rest of the marshmallow?

It turns out that bases like baking soda acts as a catalyst and increases the rate or speed at which the Maillard reaction takes place. Therefore, the baking soda and water solution caused the marshmallow to toast faster in the area where you painted the marshmallow. 

Science Extensions to Try

What do you think will happen if we use different liquids to write our hidden message? Try painting the marshmallows with:

  • Lemon juice
  • Milk
  • Vinegar
  • Plain water

Examine the marshmallows after you toast them to see how the different liquids affect the browning. 

Spoiler alert! You should see that when you write with an acid like lemon juice and vinegar, the painted area is lighter than the rest of the marshmallow. So acidic solutions slow the rate of the Maillard reaction. You can still see the secret message, but you are now reading the lighter part of the marshmallows instead of the darker part.

What do you see with the milk and plain water? Milk is also a basic solution, so it should have a similar effect as the baking soda. And since water is neutral (not acidic or basic), it should have very little effect on the browning of the marshmallow.

Final Thoughts on Marshmallow Secret Messages

Writing hidden messages on marshmallows may not be the best way to pass down secrets as a spy, but it certainly is a cool science experiment. The kids were amazed that the invisible ink (the baking soda and water solution) became visible after the marshmallows were toasted. 

Marshmallow Secret Message I _3 Dad

This may be an out of the box way for kids to show their love for their parents on Mother’s Day or Father’s Day. Imagine handing daddy a tray of marshmallows and asking him to put it in the oven on Father’s Day. How surprised would he be when the painted message shows up on the marshmallows? Plus, I bet he wouldn’t mind a piece or two of the yummy, gooey treat.


Write Secret Messages on Marshmallows with Invisible Ink Pin

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