Deconstructing the Kernel

No, not The Colonel. Though we may well get around to that particular homonym one of these days. He’s literally an institution here in Lousiville, and is in fact buried not a mile from where I’m sitting at this very moment. They say he was a very genial man who also cussed like a sailor.

But where was I now? Oh yes, the kernel. Given the topic for the week, I thought it might be useful to examine the structure of the wheat kernel a bit. You know, to see what it is about whole wheat that makes it good for you.

Technically speaking, the wheat kernel, really any cereal grain kernel, is a fruit. Some people would rather call it a berry, others a seed. Me, I think of it as an egg, which is actually more of a metaphor, but a very apt and descriptive metaphor, since the shell, white and yolk of an egg serve near identical functions to a wheat kernel’s bran, endosperm and germ.

Starting from the outside in we have the bran, which, like an egg shell, is the protective outer layer of the kernel. It’s hard and brittle, made up almost entirely of indigestible long-chain carbohydrates (cellulose), structures that are popularly known as dietary fiber. What’s so nutritious about fiber? Why, nothing at all. It’s fiber’s sheer indigestibility that makes it healthful. Impervious as it is to the processes of human digestion, it sweeps along the digestive track in a bulky mass, taking toxins and other unwanted substances with it as it goes. Which is of course why the call it nature’s broom.

Just beneath the bran is a very, very thin, oily and flavorful coating known as the aleurone layer. This layer, just a single cell or so thick, is where an astonishing amount of the kernel’s vitamins (especially B vitamins like riboflavin, niacn and thiamine) and minerals are stored. It’s the living skin of an otherwise dead mass, the endosperm.

The endosperm is the kernel’s energy storehouse, containing a mix of edible, medium-to-long chain carbohydrates (starches) and a fair amount of protein. In wheat, two of these proteins, gliadin and glutenin, are the building blocks of gluten. The proportion of protein varies from wheat strain to wheat strain. Strains with more protein are called hard wheat, strains with less are called soft wheat. They’re milled into high-gluten and low-gluten flours respectively. But I’m getting ahead of myself.

Beneath the endosperm is the germ, which like an egg yolk is the embryo of the kernel. It contains almost all of the kernel’s fat (oil), a good amount of protein, plus trace minerals and small amounts of vitamins B and E (an important antioxidant). It also contains quite a few different enzymes, which, when the kernel germinates, start busting up the place, breaking down the starches in the endosperm into sugars that the embryo can use to fuel its growth.

All in all a very neat little package. More on what happens to these different bits of the kernel in milling process as the day goes on.

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