Flour may seem, at first glance, like a boring white powder. But it’s much more than that.
To begin with, it’s likely to have been made from wheat grown right here in
But more than that, it’s scientifically interesting (something I’ve found to be true of most substances we take for granted, much to the benefit of this column).
Every grain of wheat consists of bran (the outer shell), endosperm (the bulk of the grain) and germ (the plant embryo). The endosperm consists primarily of starch granules and protein, both intended as food for the embryo as it begins to grow. White flour consists of ground-up endosperm alone: whole-wheat flour includes the bran and germ. (It also tends to go rancid faster because of a higher oil content.)
Wheat with a high protein content in the endosperm is referred to as “hard.” Wheat with a bit less protein, and hence more starch granules, is known as “soft.”
The amount of protein in wheat matters because these proteins, when mixed with water, form gluten, the substance that makes both raised bread and interestingly shaped pasta possible.
Gluten is both plastic (able to be stretched out of shape by pressure) and elastic (tends to snap back into its original shape when the pressure is released). If the gluten is of just the right consistency, it will stretch from the pressure of carbon dioxide produced by multiplying yeast, but not to the point that it breaks apart and lets the gas escape. The result: bubbles—the holes in bread that give it its delightful texture.
Durum, another kind of wheat we grow a lot of in
On a molecular level, flour contains proteins, starch, lipids, sugars and enzymes. The proteins, which from the wheat plant’s point of view are supposed to nourish the growing embryo (and instead nourish us), come in four general classes. About ten to 25 percent are albumins and globulins, which are water-soluble. The remainder, gliadin and glutenin, are not.
Protein molecules are very long and tend to fold over on themselves, linking together and forming tangles with lots of spaces into which water molecules can insinuate themselves and make weak bonds with the proteins. Stirring or kneading dough unfolds the molecules, elongating them and lining local groups of them up so they run in more or less the same direction. This makes it easier for them to form bonds with each other. This is why bread dough will suddenly get stiff and harder to work with, and become smooth and shiny.
Although proteins are vital to flour’s usefulness by making it possible for us to create bread, starch accounts for about 70 percent of flour’s weight. It comes in the form of tiny granules deposited throughout the wheat’s endosperm. In cold water, these granules don’t swell. But heat them up to around 60 degrees C, they do, and form a kind of gel with the water—which is why flour can be used to thicken sauces.
Flour contains very little in the way of fats, or lipids—about one percent by weight—but the little that is there is concentrated in the gluten and helps make it more plastic. Essentially, lipids and water seem to as lubrication, allowing sheets of gluten molecules to more easily slide past each other.
Finally, there are carbohydrates and enzymes. Sugars make up about two percent of flour’s weight, and contribute to feeding yeast during leavening—but not enough to keep it going. For that reason, flour manufacturers typically add malted wheat or barley to ground wheat. These sprouting grains contain enzymes that, when the flour is moistened, attack damaged starch granules and turn them into the sugar yeast needs.
There’s a lot going on in that “boring white powder.”
Give it some respect!
