Marshmallows seem simple when you look at them on their powdery, sugary surface. “A marshmallow is a yummy, chewy, airy confection that takes advantage of many unique food-science properties,” says Linda Wright, director of food research and discovery at the Hershey Company. “All the ingredients contribute to the delightful texture and flavor of the experience of a marshmallow.”
Whether you make them yourself or buy a bag of them, these puffy little sweets have magic to them because of the chemistry of the ingredients and how they interact.
The Key to a Gooey Marshmallow
A typical marshmallow contains sugar, corn syrup, and gelatin, plus some air. That’s it.
“A marshmallow is basically a foam that’s stabilized by gelatin,” says Richard Hartel, a food engineer at the University of Wisconsin–Madison.
In marshmallows, the foam is made up of air suspended in a liquid sugar mixture.
Gelatin is probably the most important part of a marshmallow, because it serves as the scaffolding that gives the marshmallow its stretchy, gooey texture. Gelatin is made by partially breaking down collagen, the main connective material in animal tissues, into smaller protein molecules.
“Collagen is a triple helix. It’s a helix of helices,” says Matt Hartings, a bioinorganic chemist at American University in Washington, D.C.
Collagen: A Helix of Helices
When you’re making marshmallows, one of the first things you do is add the gelatin to warm water. The heat breaks down the bonds holding the helices’ polypeptide chains together, causing the protein strands to partially unravel and spread out in the water, Hartings says. As the water starts to cool, parts of the gelatin molecules wind back together in threes, making up that helix of helices. Some parts of the gelatin, however, don’t wind back together and instead remain floppy and flexible. This structural mix of bendy and firm parts is what gives gelatin its elasticity, perfect for making bouncy foods like marshmallows.
This elasticity is hard to simulate, Hartel says. Vegan marshmallows do exist, and they use soy protein and carrageenan instead of gelatin. Carrageenan, which comes from seaweed, consists of chains of polysaccharides that form helices. Together with soy protein, it gives the ani-mal-product-free marshmallows a bouncy texture similar to that of gelatin-based marshmallows, although not quite as firm.
Another useful characteristic of gelatin is that it forms a thermo-reversible gel, which means that it can flip back and forth between liquid and gel depending on the temperature.
“The melting point of gelatin is about 95 °F (35 °C), which is just below normal body temperature,” Wright said in an email. “This contributes to how marshmallow melts smoothly in the mouth when eaten.”
Candymakers can change the texture of gelatin-containing foods by varying how much gelatin they use, Hartel says. For example, marshmallows and gummy bears are both made of gelatin, corn syrup, and sugar.
“We use more gelatin in a gummy bear than we do in a marshmallow, because we want the gummy bear to have firm characteristics,” he says. In a gummy bear, the gelatin forms a gel structure by itself. In a marshmallow, there’s another key component: air.