When we put toast in the toaster or add marshmallows to the top of our sweet potatoes for a baked holiday dish 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.
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 take 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 when 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)
- Toaster oven or regular oven
- Baking soda
- Lemon juice
- Five small paper cups
- Paper and pen or pencil
- Measuring spoon (tablespoon)
- Permanent marker
- Baking tray (or tray for toaster oven)
- An adult helper
- Use your marker to number the paper cups with 1–5.
- Create a table that lists "Number on Cup" in the left column, with each cell below labeled 1, 2, 3, 4 and 5, respectively, and "Liquid in Cup" in the right column, with each of the following liquids listed in this order: water, baking soda, vinegar, milk and lemon juice. So 1 should line up with water, 2 with baking soda, and so on.
- Add at least three tablespoons of each of your liquid ingredients to the designated cup, using the table as a reference. For the baking soda, add one tablespoon of baking soda to five tablespoons of water and stir.
- Place a clean Q-tip in each cup.
- Cover your baking tray in tinfoil.
- Arrange your 10 marshmallows on your baking tray in two rows, five marshmallows across.
- On the first column of two marshmallows, use your Q-tip dipped in water to paint the number 1 on each marshmallow.
- On the second column of two marshmallows, use your Q-tip dipped in baking soda to paint the number 2 on each marshmallow.
- On the third column of two marshmallows, use your Q-tip dipped in vinegar to paint the number 3 on each marshmallow.
- On the fourth column of two marshmallows, use your Q-tip dipped in milk to paint the number 4 on each marshmallow.
- On the fifth column of two marshmallows, use your Q-tip dipped in lemon juice to paint the number 5 on each marshmallow.
- 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. Do you have any guesses as to what you might see on the marshmallows painted with different liquids?
- Monitor your marshmallows constantly—they will brown very quickly!
- 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!
- 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? Thinking about the various liquids, what do you see that might be similar about the liquids that made the lighter or darker numbers?
- Extra: Repeat this activity with other safe, edible household products that you can paint onto your marshmallows. Try toothpaste, over-the-counter antacid remedies or other types of fruit juice.
Observations and results
In this activity you examined how five different solutions affected 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.
Once the marshmallows have cooled completely, they can be handled and are safe to eat, store for later or to share with your helper.
More to explore
The Sweet Beginnings of Caramelization, from Science Buddies
Making a Sugar Thermometer, from Scientific American
Making Maple Syrup Candy: How Does Temperature Affect It?, from Science Buddies
Sweet Science: Making Marshmallows, from Scientific American
Science Activities for All Ages! from Science Buddies
This activity brought to you in partnership with Science Buddies