Corn kernels (when dry not like corn on the cob) have a hard outer shell that water can’t get through. There is a bit of water inside the kernel and when you heat the corn this water heats up and tries to turn to steam. Because the kernel’s shell is solid the steam can’t get out and the pressure keeps building until it pops.
The white fluffy stuff is made of starch and protein. When the kernel is being heated this become soft and mushy, when the kernel pops the steam which was previously trapped inside and in amongst all the starch rushes out and in the process inflates the white stuff we eat. This cools pretty quickly (compared the the sealed kernel) and so solidifies in to a delicious fluffy shape.
Popcorn has been popped by humans probably as far back as 6,700 years ago in Peru. These days popcorn is popped by adding a little oil or butter to the grains of maize (the variety of corn used) which helps transfer the heat to the kernels, although air poppers are now also available.
My wife Helen worked for a summer for a Chicago-based company called Popcorn Palace, which sells 29 different flavoured popcorns like white chocolate peanut butter and spicy cheese. Sometimes, at the end of the day she would bring home black refuse sacks full of leftover popcorn for the 7 of us who shared our tiny flat.
After that summer I couldn’t even look at popcorn for months, I was so sick of it. I love it now again, though…