The difference between cereal marshmallows and regular ones is all in the water and how you whip it.
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What is a marshmallow? You've probably never had to give it much thought. Like Supreme Court Justice Potter Stewart’s definition of obscenity in Jacobellis vs. Ohio, it’s kind of an “I know it when I see it” situation. But here’s something worth pondering: How exactly are the marshmallows you’d buy in a bag and roast over a campfire different from the kind you’d find in, say, a box of Lucky Charms?

It turns out what differentiates your puffed-up bag marshmallows from their smaller cereal counterparts is a matter of a few ingredients. According to Lucky Charms’ packaging, your favorite hearts, stars, and horseshoes are made up of sugar, modified cornstarch, corn syrup, dextrose, gelatin, and calcium carbonate. On the other hand, the big, fluffy marshmallows you’ll find on store shelves feature corn syrup, dextrose, modified cornstarch, sugar, natural and artificial flavorings, gelatin, water, and a whipping aid known as tetrasodium pyrophosphate.

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To expert confectioners, it’s those last two ingredients that make the biggest difference. The water obviously makes for a less dehydrated marshmallow. Without the help of a whipping aid, it’s not possible to mix up the heated sugar and gelatin properly to give the mixture its defining shape and squishy texture.

Given those differences, do the marshmallows in breakfast cereals like Lucky Charms even count as real marshmallows? It depends on who you ask. “A marshmallow is like a sweet, gooey, fluffy cloud,” Leen Kim, the executive chef at Hot Springs, Virginia’s Omni Homestead Resort, told "In my opinion, marshmallows in cereals are more like candy simply because they are dehydrated."

Conversely, baker Alison Mahoney believes that while cereal marshmallows fit the definition of a marshmallow. She tells that all marshmallows should technically be classified as candy. She also points out that there’s likely more cornstarch in cereal marshmallows, since that could help them stay shelf stable while keeping their compact shape.

So there you have it: turns that cereal marshmallows are dehydrated and unwhipped, but maybe all marshmallows are candy. Even if sugary cereals are all the rage, don’t expect General Mills to publicly cop to that last idea any time soon.