Key concepts
Boiling point
Food science

Whether you're gathered around a fire or drinking hot chocolate after a day in the snow, nothing says sweet, squishy fun quite like a marshmallow! Even its name is soft and spongy! Have you ever wondered how marshmallows are made? Long ago people made marshmallows with ingredients from the marshmallow herb, but today we usually make them with other ingredients, namely gelatin, corn syrup and sugar. In this appetizing activity you'll get to explore what ratio of sugar to corn syrup produces the best-tasting and best-textured marshmallows!

Marshmallows are an unusual type of sweet treat—spongy, sticky and a little bit chewy. They have a melting point that is just above body temperature so that they start to change from a solid to a liquid state as soon as they reach the warmth of your mouth—or the heat of a fire! They're also an ancient creation, originally coming from a tall marshmallow plant (Althaea officinalis) that grows in swampy fields and has a soft, spongy root. Its root contains mucilage, a thick, gluey substance produced by some plants and microscopic animals to help with food storage and seed germination. Some cultures used the plant to make candy, whereas others used it to make medicine. The ancient Egyptians, for example, dried the root and mixed it with honey to make marshmallow treats, but the French experimented with using its gummy juice to soothe sore throats.

Modern marshmallows no longer contain parts of the marshmallow plant. Instead, the store-bought version is primarily a mix of three ingredients: sugar, corn syrup and gelatin. The gelatin replaces the thick, gluey substance from the marshmallow plant. Varying the ratio of sugar to corn syrup can significantly affect what the resultant marshmallows are like.

•     Timer
•     Two square foil cake pans or round foil pie pans each eight to nine inches wide
•     Masking tape
•     Pen or marker
•     Vegetable oil, such as canola or safflower oil
•     Paper towels
•     Powdered or confectioner’s sugar
•     Small strainer
•     Large mixing bowl
•     Measuring cups
•     Water
•     Two plain, unflavored, quarter-ounce gelatin envelopes; available at grocery stores
•     Fork
•     One half cup of corn syrup, like light corn syrup; glucose syrup is a possible substitute
•     One and one quarter cups of granulated sugar
•     Small saucepan with lid
•     Candy thermometer (must be able to read up to 240 degrees Fahrenheit, or about 115 degrees Celsius)
•     Electric mixer or beater
•     Measuring spoons
•     Pure vanilla extract
•     Spatula
•     Pizza wheel or cookie cutter approximately one-by-one inch
•     Ruler
•     Large airtight containers or gallon-size sealable plastic bags
•     Taste-testing volunteers (such as friends and family!)

•     Wash and thoroughly rinse your hands.
•     Set out all cooking tools and ingredients so they are ready to go and easy to access.
•     Use the masking tape and a pen or marker to label the bottom of one cake pan "1" and the other "2."
•     Pour a small amount of vegetable oil on a paper towel and lightly oil the inside of the cake pans. Pour a small amount of powdered sugar in the strainer and lightly dust the inside of the pans.
•     Be careful when heating syrup mixtures in the saucepan. An adult should closely supervise these steps.

•     Pour one sixth cup of cold water into the large mixing bowl. (To get one sixth cup, just fill up the one third measuring cup halfway.) Sprinkle a quarter-ounce packet of gelatin over the cold water. Mix the gelatin and water together for about five seconds with a fork and set the bowl aside. This will give the gelatin time to soften, or "bloom."
•     Add one quarter cup of cold water, one half cup of sugar, and one third cup of corn syrup to the saucepan. (This is a 3:2 ratio of sugar to corn syrup.)
•     Put the lid on the saucepan and turn the stove to medium-high heat. An adult should closely supervise all work from this point on. The syrup solution, which will become very hot, should be handled with extreme care.
•     Lift the lid and check the solution in the saucepan about every 30 seconds until it just comes to a boil. Remove the lid.
•     Begin to measure the temperature of the syrup in the saucepan using the candy thermometer. Do not let the thermometer touch the bottom or side of the pan, but instead try to put the tip below the surface, near the middle of the pan. Continue heating your syrup until the temperature reaches 240 degrees Fahrenheit (about 115 degrees Celsius). How does the temperature rise? Does it go up quickly at first? What happens as the syrup becomes more concentrated?
•     When the temperature reaches 240 degrees F, immediately turn off the stove and move to the next step. How does the syrup mixture seem to change as it gets closer to this temperature?
•     Turn the mixer on low and carefully pour the hot syrup into the large mixing bowl with the gelatin. (Some syrup will likely solidify on the saucepan.)
•     Set the timer for 11 minutes and start it.
•     Gradually increase the speed of the mixer until it is operating at full (high) speed. Continue to beat for approximately 11 minutes, or until the mixture starts to become very thick, glossy and lukewarm. How does the mixture change as you mix it?
•     Add one half teaspoon of vanilla extract and then beat for one more minute. Note how long you beat the syrup.
•     Quickly use a vegetable oil–coated spatula to scoop out the marshmallow mixture from the mixing bowl and put it into the prepared cake pan labeled 1. If needed and easy to do, use the spatula to gently smooth down the top of the marshmallow so that it is pretty flat.
•     Wash and dry all cooking utensils.
•     Repeat the entire activity procedure (not including the preparation) but this time add a three quarter cup of sugar and one sixth cup of corn syrup to the saucepan. (This is a 9:2 ratio of sugar to corn syrup.) (Still add the one quarter cup of cold water to the saucepan first.) In the mixing bowl beat this recipe for the same amount of time. When it is ready, scoop this marshmallow mixture from the mixing bowl and into the prepared cake pan labeled 2.
•     Allow the marshmallow "pies" to sit out, uncovered, on a counter for at least four hours (or as long as overnight) so they can become firm.
•     Once firm, turn the marshmallow pies over, one at a time, onto a cutting board. Use a spatula to help lift the pies out.
•     Roll a pizza cutter or cookie cutter into some powdered sugar and then use it to cut up your marshmallows into approximately one-by-one-inch pieces.
•     Dust the marshmallows on all sides with a little strained powdered sugar.
•     Place the marshmallows in an airtight container or plastic bag, labeling the container with the number of the recipe (1 or 2).
•     Within a week of making the marshmallows, take a marshmallow piece from each bag. Try to find pieces that are as similar in shape and size as possible. Drop each marshmallow in a saucepan of hot water, keeping track of which marshmallow was from each recipe. Watch and see how quickly each marshmallow piece melts. Repeat this melting test three times. Which marshmallow piece melted first?
•     Within a week of making the marshmallows, gather your taste-testing volunteers (such as family and friends) to evaluate the marshmallows for taste and texture. Which marshmallows do they prefer? Which ones are the chewiest and which ones are the least chewy? Which are the softest and which are the hardest? You may want to save a few pieces to do some of the "Extra" tests below.
•     Extra: In this activity you may have noticed that marshmallow pieces were harder from one recipe than the other. You can try to investigate this more quantitatively. To do this, put a marshmallow square from one of the recipes on a cutting board. Arrange a small cookie cutter so that it can sit on top of the square. On top of the cookie cutter balance a small plastic or paper cup. Put 20 pennies in the cup, one at a time. Did the cookie cutter leave a noticeable impression? Try this with a marshmallow square from the other recipe. Did the cookie cutter leave a more or less noticeable impression?

Observations and results
Were the marshmallow pieces from recipe 1 fluffier, softer and less sweet than the pieces from recipe 2? Did the marshmallows from recipe 1 melt faster than the pieces from recipe 2?

In the sugar and corn syrup solutions you heated, the sugar made the solutions' boiling points higher than that of pure liquid water. The greater the concentration of sugar in the solution, the higher its boiling point. Consequently, marshmallow pieces from recipe 1 should have had a lower boiling point than pieces from recipe 2, making the former melt faster than the latter when placed in hot water. The final concentration of sugar in the syrup determines the structure of the candy that forms. Think about caramels and lollipops—the caramel is softer and chewier whereas the lollipop is hard and cracks when you bite it. The syrup used to make caramels is cooked until it has about an 87 percent concentration of sugar in solution, whereas the syrup used to make lollipops reaches about 99 percent concentration of sugar in solution. (As the syrup boils water evaporates, and the syrup becomes even more concentrated with sugar.) When making marshmallows, the syrup is cooked until an 85 percent concentration of sugar is in the syrup, and the corn syrup is added to help prevent crystals from forming in the cooled syrup. The marshmallow pieces from recipe 1 should have been fluffier, softer, less sweet and more like store-bought marshmallows than the pieces from recipe 2.

Gelatin is a protein that comes from collagen, the main protein in connective tissue in animals. It has the special quality of being able to coagulate (or come together) when it is beaten or whipped. When the hot concentrated syrup is beaten into gelatin with a mixer, bubbles form in the mixture and the gelatin coagulates around the bubbles, stabilizing their walls so they don't collapse.

Enjoy your tasty marshmallow treats! If stored in an airtight container, they should be good for a week. To clean up any marshmallow-making messes, try dissolving and washing them away with warm water.

More to explore
Monster Mallows from the Exploratorium
The Cold Water Candy Test from the Exploratorium
Test Recipes: Marshmallows from Michael Chu at Cooking for Engineers.
Mixing Your Own Marshmallows: Finding the Right Ratio of Sugar to Corn Syrup from Science Buddies

This activity brought to you in partnership with Science Buddies