It’s a corny time of year, this pause between summer and fall, what with all the fresh-picked local corn around. (Eat it quickly — half its natural sugar can turn to starch within 24 hours.) Then there are all the earnest “spirit-of” festivals and fairs and their incumbent corn dogs, corn-on-a-sticks slathered in yellowish oil, kettle corn, and the endless treats spun from corn syrup.
Corn, more properly called maize, has become a very political creature in the food activist world, sucking up, as it does, endless tracts of fertile farmland and converting them to petrochemical-laced monocultures.
But it also has a more innocent and fundamental side, steeped in pre-history alongside wheat and rice as the three cereal grains that have kept humankind in its caloric frenzy.
There are five main kinds of corn, and a handful of others. Dent corn, so-named for the dent on top of the kernel, is softer and usually grown for animal feed and milled corn products, such as grits and corn meal. The flour corns, including blue corn, are easy to grind; sweet corn is the variety we eat.
But popcorn is the most playful corn, and possibly the source of all modern corn varieties, via the primal corn ancestor, a messy looking grass plant called teosinte . Popcorn is a special type of flint corn, so named for their hardness. All flint corn (also called Indian corn) has relatively large amounts of storage protein surrounding the granules of starch.
In a nutshell — or a kernel — the simple take on how popcorn pops is heat makes the moisture inside the kernel expand. But this belies the fascinating science beneath the hull, so to speak. And for this I turn to Harold McGee’s wonderful book, On Food and Cooking .
Some varieties of flint and dent corn will “pop”, but they expand far less than true popping varieties, which are generally smaller and contain more hard, translucent endosperm inside the hull (the endosperm is the fleshy white or yellow bit that makes up most of the kernel).
Popping varieties, and there are many — for instance, microwaveable popcorn is a different variety than movie popcorn — have another built-in feature that makes them pop better. Because the popcorn hull is denser, it conducts heat several times faster than the hulls of other corn. And because they are denser and thicker (ergo so annoying when you get them stuck in your gums), they can also withstand more steam pressure before they give way and the kernels explode.