(Image credit: Erin Alderson)

A pantry staple, flour is an ingredient you might not have given much thought. But these days, there's a surprising selection of flours in your grocery store's baking section. There's all-purpose of course, but also pastry flour, cake flour, and bread flour. You can also choose between bleached and unbleached, white and whole-wheat — and then there's the wide world of alterna-grain (i.e., non-wheat) flours. But do you actually know what flour is?

To put it succinctly, flour is a powder ground from grains — typically wheat. To get a bit more, ahem, granular, when we talk about grains, we're usually talking about the edible seeds harvested from cereal plants. And these seeds have three parts: the bran, the germ, and the endosperm. The bran protects the seed until it is ready to grow. The germ is where growth begins, and the endosperm stores the stuff that a plant uses as food.

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We want that food, too, so we hijack the stored energy in the form of proteins commonly known as gluten. If you want to get really geeky, gluten is made up of two types of protein: gliadin and glutenin. The ratio of these components vary, and some combinations are better than others at making bread rise.

To turn grain into flour, it needs to go through a milling process. How that all works is the subject of another story, but the end result is that the grain is broken down into tiny pieces and, typically, there is a very clean separation of the three main parts of the wheat kernel (the germ, the bran, and the endosperm).

White flour is made from the endosperm only — the bran and germ are sifted off and become different products — while whole-wheat flour is most often made by recombining the endosperm with the germ and the bran once the germ is stabilized. The germ and the bran contain fats that spoil quickly, which is why whole-grain flours have a shorter shelf life.