A skin you cannot digest
Why Does Sweetcorn Come Out Whole?
Sweetcorn appears again the next day because each kernel is wrapped in something your gut has no tool for.
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Step 1 of 5
Cellulose is a sugar your body cannot open.
Plants build their walls out of cellulose, which is glucose joined in a way human enzymes cannot cut. Cows manage it with help from bacteria; we simply do not.
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Step 2 of 5
A kernel is a seed, and seeds are built to survive.
Every kernel is a corn seed, and a seed's job is to get through an animal intact and come out somewhere useful. Being indigestible is not a flaw.
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Step 3 of 5
The inside is digested normally.
The starch and sugar inside the kernel are absorbed like any other food. Only the empty skin makes it through, which is why what you see looks hollow.
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Step 4 of 5
Chewing changes it.
Break the skin and the inside spills out, which is exactly what teeth are for. Corn chewed properly mostly does not reappear — it is a chewing problem as much as a gut one.
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Step 5 of 5
Indigestible plant matter is still useful.
Fibre does its job precisely by not being absorbed. Cellulose passes through without feeding you, and that bulk is what keeps everything moving. It is called fibre precisely because it is the part you cannot use.
Sweetcorn is a mutant field corn that fails to convert its sugar into starch. Picked late, it goes starchy and dull within hours.
The short version
A corn kernel's skin is cellulose, which no human enzyme can cut, so the wrapper survives while the inside is absorbed.
Try it yourself
Squash a cooked kernel between two fingers. The soft inside comes out and a thin transparent bag is left.