You already know two corns — the sweet one on your plate and the field corn grown for animals and fuel. There is a third kind, and it is the only one that blows itself inside out.
Popcorn is one of the oldest types of corn, and it is built differently from the rest. Inside is a hard endosperm wrapped around a small amount of soft, moist starch. Outside is a tough shell called the pericarp — and that shell is the whole secret. It is the reason a popcorn kernel pops and a kernel of sweet corn or field corn does not.
Basis: Michigan State University Extension (4-H, “Exploring your world: Popcorn!”): popcorn “is one of the oldest types of corn and contains a hard endosperm surrounding a small amount of soft moist starch.” Purdue University College of Agriculture: “The hard outer hull of popcorn, called the pericarp, explains why 1.5 percent of the state’s corn pops while none of the rest can.”
The other half of the secret is water. A popcorn kernel has to carry a specific amount of moisture inside it — roughly one part in seven of its own weight. Too dry and there is nothing to turn into steam; too wet and it will not pop properly either, so the water inside has to stay inside a narrow band.
Basis: Purdue University College of Agriculture: “Popcorn must have moisture inside the kernel of about 13 to 14.5 percent of its total weight.” Michigan State University Extension: “The best popcorns have a moisture content between 13.5-14 percent.”
Now heat it. As the pan or the microwave pushes the kernel toward about 450°F, the water inside turns to steam and the pressure climbs, held in by that tough shell. When the shell finally cannot hold any more, it bursts — and the starch, now hot and gooey, expands in an instant and sets as white foam. The kernel has literally turned inside out.
Basis: Michigan State University Extension: “As the cooking temperature rises to about 450 degrees Fahrenheit, the moisture inside the kernel turns to steam and pressure begins to build. When the shell cannot withstand the pressure any longer, it ‘POPS!’” Purdue University: “When the pressure reaches a certain point, the outside layer of the kernel ruptures and the kernel pops with a rapid expansion of the now gelatinizing starch” — “essentially, the kernel turns inside out, giving popcorn its distinct look.”
Next to the giant field-corn harvest, popcorn is a small specialty crop: even in Indiana, the state at the top of this table, only a sliver of the corn fields was popcorn. So a state can be a corn giant and still be nowhere near the top of the popcorn table.
Basis: Purdue University College of Agriculture: in Indiana in 2019, popcorn was grown on only a small fraction of the state’s corn acres.
So why do these particular states lead? Popcorn is usually grown on contract for a company that dries, tests and packs it, and those plants sit in a handful of places. Once the buyer, the dryer and the packing line are nearby, the next farm has a reason to plant popcorn there too. That is a story about businesses and neighbours, and a table of pounds cannot prove it.
※ A hypothesis is an idea that isn't proven yet.
📊 Sources for the rankings mentioned in this note (links to the original data and retrieval dates) are on each quiz page below.