All-purpose flour is a general use white flour. It is not a whole flour, and only the starchy endosperm is used, without the germ and bran portion of the kernel. It is a blend of hard and soft flours or hard flours with a protein content (gluten) of about 9 to 12 percent. It is sometimes called, for short, AP flour.
Hard flours are flours like bread flour, which contain more gluten, and soft flours are flours like cake flour, which contain less gluten. All-purpose flour is meant to be an intermediate between these two, suitable for most baking needs. It was developed so that the home cook could use one flour for everything from bread, to cakes and pastry. Ideally, cakes are made with a softer cake flour and bread is made from a harder bread flour, but since most consumer grocery stores have all-purpose flour available, but not necessarily any specialty flours, most cookbooks call for all-purpose flour in most baking recipes. All purpose flour is suitable for making cookies, biscuits, popovers. It will yield satisfactory results in most baking recipes but a specialty flour is best for serious bakers.
A cake made with all-purpose flour may have too much gluten, making it tough and dense. Bread made with all-purpose flour may not have enough gluten, making it too fragile.
All-purpose Flour in the South versus the North
All-purpose flours vary regionally, based on the type of baking most often done in a particular part of the country. Generally, all-purpose flours in the Southern United States will be softer, since southerners tend to make more biscuits, and a softer flour yields a lighter, fluffier biscuit. Northern all-purpose flours have a higher proportion of hard flour. Most all-purpose flours will report approximately the same amount of protein on the nutrition label, at 3 grams protein per 1/4 cup, which is 12% protein, which is on the high end of ‘medium’. Gold Medal®, Pillsbury®, and Martha White® (Southern) all-purpose flours all contain 12% protein, suitable for most baking needs. King Arthur® all purpose flour contains a higher amount of protein than most grocery store brands, at 13%. White Lily® flour, a Southern brand, contains only 8% protein, which places it into cake flour range, making it great for biscuits and pastries, but not really an “all purpose flour.”
Bleached and Unbleached
Bleaching is a chemical process used to make the flour whiter in appearance and to improve it’s functional properties. Freshly milled flour is not white, but bleaching does not yield results that are as good as aged flour. Aging serves to naturally bleach the flour through oxygenation, which also serves to improve the gluten. However, this is a costly process, involving a great deal of storage space, labor, and a high risk of pest infestation. Chemical bleaching, such as with chlorine gas or benzoyl peroxide, is much less expensive. This bleaching lightens the flour and also improves the strength and elasticity of the gluten by increasing the number of disulfide bonds. Unbleached all-purpose flour is only marginally darker unbleached products are now available in most large chain grocery stores. The volume, texture, and crumb structure is also improved.
Although some consumers turn to unbleached flour out of health considerations, there is no residue left from the bleaching agents on bleached flour. It is, instead, the cost to the environment that consumers should be concerned about.
Flour Bleaching and Nutrient Loss
There is a consistent myth, reported by various sources, that chemical bleaching removes vitamins from flour, which must then be added back in through fortification. Although bleaching does destroy some additional vitamin B6 and folic acid, the milling process itself, which removes the nutritious bran germ, is the reason that white flours began to be fortified. A casual check of the nutrition labels on both bleached and unbleached flour products should put this myth to rest, as they are all fortified, usually with niacin, iron, thiamine mononitrate (Vitamin B1), riboflavin (Vitamin B2), and folic Acid (Vitamin aB).
All “white” flour is “bleached”. Unbleached flour is bleached through aging. Some consumers are easily fooled, however, into thinking that modern unbleached products are then chemical free. However, potassium bromate is sometimes used as a maturing agent and is a known carcinogen. Although it was once believed that all bromates were removed through heating, it was later found that trace amounts remained in baked products. Since then, it has been phased out by many producers in favor of ascorbic acid, and many countries have banned its use.
The simple fact is, however, that in terms of nutrition, there is no significant difference whatsoever between bleached and unbleached flour. It is quite silly to quibble about the nutritional value of one white flour over another, when white flour, by definition, has had most of it’s micronutrients removed through the milling process, and then added through fortification. It is the functional characteristics of the flours that are different, and the environmental impact of the bleaching process.