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Invisible Marshmallow Ink – Send Sweet Secret Messages Using Marshmallows!

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Key Concepts
Acids, bases, Maillard reactions
Teisha Rowland, PhD, Science Buddies


When we put toast in the toaster, or add marshmallows to the top of our sweet potatoes at Thanksgiving, we expect them to turn brown, and to develop a sweet, caramelized flavor. Although we expect it to happen, do you know why certain foods take on these new colors and flavors as they are toasted? In this activity you will explore the reaction that creates these tasty, toasty treats, and experiment with speeding up and slowing down the process.

This activity is not recommended for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.


The process of toasting foods that we enjoy takes place because of a phenomenon known as the Maillard reaction (named after its discoverer, Louis-Camille Maillard). This reaction is actually a sequence of multiple reactions that takes place between proteins and sugars when we heat our food. When the reactive carbonyl group of the sugars in the food react with the amino group of the protein, a series of new molecules are created. These new molecules contain hundreds of different flavor and aroma compounds that give rise to the caramel flavors and scents we associate with toasting.

Foods can turn brown for a number of reasons that happen outside of the Maillard reaction. When chicken turns black on the grill, or sliced fruit begins to brown when left out, other chemical reactions are at work. The Maillard reaction is important for baking, because it turns our cookies and breads that delicious golden color that we’ve come to expect.

In this activity you’ll be exploring the Maillard reaction, and how you can speed it up and slow it down with some simple kitchen chemistry!


  • Marshmallows (at least 10)
  • Q-tips
  • Toaster oven or regular oven
  • Baking soda
  • Milk
  • Lemon Juice
  • Vinegar
  • Water
  • 5 small paper cups
  • Measuring spoon (tablespoon)
  • Permanent marker
  • Baking tray (or tray for toaster oven)
  • Tinfoil
  • An adult helper


  1. Use your marker to number the paper cups with 1-5.
  2. Add at least 3 tablespoons of each of your liquid ingredients to each cup, in this order: 1- Water, 2- Baking soda, 3- Vinegar, 4- Milk, 5- Lemon Juice. For the baking soda, add 1 tablespoon of baking soda to 5 tablespoons of water and stir. 
  3. Place a clean Q-tip in each cup.
  4. Cover your baking tray in tinfoil.
  5. Arrange your 10 marshmallows on your baking tray in two rows, five marshmallows across.


  1. On the first column of two marshmallows, use your Qtip dipped in water to paint the number ‘1’ on each marshmallow.
  2. On the second column of two marshmallows, use your Q-tip dipped in baking soda to paint the number ‘2’ on each marshmallow.
  3. On the third column of two marshmallows, use your Q-tip dipped in vinegar to paint the number ‘3’ on each marshmallow.
  4. On the fourth column of two marshmallows, use your Q-tip dipped in milk to paint the number ‘4’ on each marshmallow.
  5. On the fifth column of two marshmallows, use your Q-tip dipped in lemon juice to paint the number ‘5’ on each marshmallow.
  6. Ask your adult helper to carefully place your tray in the oven on the top rack. Have your adult helper set the temperature to ‘Broil’.
  7. Monitor your marshmallows constantly – they will brown very quickly!
  8. When the marshmallows have toasted a warm brown color, have your adult helper remove them from the oven. Caution – the inside of the marshmallows will be extremely hot – do not eat or touch them until they have cooled!
  9. Examine the surface of your marshmallows. Can you see the numbers that you painted on the marshmallows? Which numbers can you see? Which numbers are not visible? Are the numbers all the same color, or are some darker than others?

Extra: Repeat this activity with other safe, edible household products that you can ‘paint’ onto your marshmallows. Try toothpaste, over the counter antacid medication, other types of fruit juice.

Observations and Results

In this activity you examined how 5 different solutions affect the rate of marshmallow toasting. You should have observed that for some of the solutions, the numbers written on the marshmallow appear darker than the rest of the marshmallow. In contrast, for other solutions, the numbers appear lighter than the rest of the marshmallow.

In the case of the darker numbers, the solution caused the marshmallow to toast faster in the area where you painted the marshmallow. This tells us that in this case, when the number is darker, the solution increased the rate of the Maillard reaction. In contrast, when the number on the marshmallow appears lighter than the rest of the marshmallow, we can determine that the solution decreased the rate of the Maillard reaction.

Did you notice any patterns related to which solutions caused the number to darken, and which caused the numbers to lighten? It turns out that basic solutions (such as baking soda and milk) speed up (or catalyze) the rate of the Maillard reaction. In contrast, acidic solutions (such as lemon juice and vinegar) slow the rate of the Maillard reaction. Therefore, you should have found that the numbers 2 and 4 looked darker than the surrounding marshmallow, whereas the numbers 3 and 5 appeared lighter than the rest of the marshmallow. Because water is relatively neutral, the number 1 may have appeared very faint, or not shown up at all on the marshmallow.

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