The science behind a perfectly-toasted marshmallow


Wilderness is nice, but hands down, the number one reason to go camping is to incinerate food over a fiery pit. Everything tastes better when it’s burned over flames, especially marshmallows. But before you dip your ‘mallow-tipped toasting fork in the campfire, here are a few things you should know:

Marshmallows are sugary gas bags

Marshmallows are mainly sugar, but air actually makes up more than half their volume. They’re made by beating together gelatin or another gel-forming ingredient with a hot sugary syrup. Beating the mixture creates air bubbles, which become trapped as the liquid mixture cools into a gel — creating the spongy texture.

Those bubbles are why Peeps explode in the microwave, and flaming marshmallows swell on the end of a toasting fork. Hotter temperatures makes the air trapped inside the marshmallow expand and take up more space, forcing the flexible sugary mixture to stretch. Eventually, if the pressure is too much? Kaboom.

But take the marshmallow out of the heat, and it’ll deflate — although the stretched out gelatin doesn’t bounce back. “It shrinks to a shriveled mass,” Richard Hartel, a food scientist at the University of Wisconsin-Madison, tells The Verge in an email. “Don’t get me started on Peeps jousting.”

The best marshmallow is a burnt marshmallow

Well, maybe not burnt — but definitely toasted. Heating the marshmallow over the fire can make the sugar caramelize, a chemical reaction that produces the brown color and toasted flavor. It requires really high temperatures, so microwaving your marshmallow isn’t going to cut it.

“Many foods don’t get hot enough when they cook for caramelization (like bread),” food chemistry professor Matt Hartings at American University tells The Verge in an email. “Marshmallows certainly do over a fire.”


When the sugar gets hot enough, it starts to break down into smaller molecules that then react with one another. These reactions produce new fruity, nutty, and buttery flavors you can taste and smell on your toasted marshmallow. They also turn the marshmallow skin that satisfying golden color.

Certain sugars may also react with amino acids in the gelatin in what’s known as the Maillard reaction. It occurs at much lower temperatures than caramelization and contributes to the rich brown color and complex flavors of a seared steak, roasted coffee, or caramel candies. For marshmallows that are very slowly roasted, Hartel suspects that the Maillard reaction might be what’s producing their golden hue and general deliciousness.

Maximal goo requires patience

Marshmallows start to melt when they heat up to just above body temperature, Hartings says. But if you’re not careful, you can completely burn the outside before the inside even gets warm. The heat of the fire shakes loose the chemical bonds in the gelatin that hold the candy together, which makes the marshmallow ooze.

So, whether you prefer marshmallows golden brown or charbroiled, don’t catch them on fire immediately if you want to maximize the gooeyness. “You’ve gotta be patient and slow for a while (letting the meltiness reach all the way to the insides). Then,” Hartings says, “you can torch the sucker.”




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