I was having a discussion with another Brian at a bar late last year, and the subject of wheat and flour came up (as it so often does). As the discussion wended this way and that, I realized that there was some confusion about the types of things that you can do to wheat in order to turn it into flour. The two big issues were whole wheat flour vs. regular wheat flour vs. unbleached wheat flour. So, let’s take a quick tour of wheat processing.
Most of what wheat goes through in processing is mechanical. There are several stages of cleaning and sorting to make sure you don’t get bug flour or steel flour or anything like that included in your baked goods. Then you have a general pulverization of the wheat to sort out the three main components of the edible part of wheat: the bran, the endosperm, and the germ.
In the case of your typical, fully-processed all-purpose white flour, you are getting just the endosperm that has been further worked upon by the various machinery. In the case of whole-wheat flour, you are getting the bran and the germ as well. So from a whole-wheat vs. white flour perspective, the difference is strictly mechanical.
Of course, nutritionally, you’re giving up a lot by going with the white flour. Whole wheat has a lot more fiber, which is usually what people think of when they think whole wheat bread. You get that primarily from the bran, which is the outer coating of the wheat. Then there are a number of nutrients and some oil in the germ. The germ needs all of that because that is the working part of the wheat seed; its job is to sprout more wheat when the time comes. The endosperm, which is the primary component of white flour, is basically the energy source for the wheat, holding all the starches and proteins. So there are good reasons, from a nutritional perspective, to go with whole wheat.
Flour can go through another stage of processing, called maturation. There are two types of maturation in flour, the kind to increase the amount of gluten in a flour and the kind to decrease it. If you’ve heard of flour that’s been bromated, that is a method of increasing the amount of gluten in flour, though I can’t recall the last time I’ve seen bromated flour. There was concern in the ’80s that it could cause cancer, and the FDA encouraged bakers in the US to stop using the process. Several other countries have banned bromated flour. Nowadays, many people use ascorbic acid (Vitamin C) to increase the gluten in their flour. Some recipes for bread by Alton Brown and Shirley Corriher even have you crush up some Vitamin C tablets to make your bread more likely to succeed. It’s not as effective at increasing gluten as potassium bromate, but it’s a lot better for you.
On the opposite end of maturation is bleaching. Flour refiners use this process on cake flour to reduce its gluten content. For that, they use chlorine gas. The chlorine gas also allows the starch molecules to absorb water more easily, making for a moist cake. I don’t know how much of the chlorine makes it to your cakes, but as far as I know it’s a lot less than, say, what’s in your drinking water, so it’s probably not a terrible thing overall. I know we’ve discussed this before, but it’s important to remember with poisonous chemicals in food that everything will kill you in the right concentration, so just because it’s poisonous doesn’t mean you can’t have a little bit of it here and there.
In higher-gluten flours, such as bread flour, the only reason to bleach is to make the flour look whiter. For this, refiners use benzoyl peroxide. It does not affect the starch, it does not affect the gluten content, it’s just to make the flour look more white. I do not approve of this at all. “Oh, no! My bread is a vaguely dingier shade of beige when I want it to be white as the un-driven snow!” Bah. Yes, yes, we eat with our eyes first, but seriously: natural foods are pretty, too. Get your bread flour unbleached.