What do I need to know about flour?

There are several “types” of flour available on the supermarket shelf.  They have different components which perform different functions, making them suitable for different types of recipes. These components vary, depending on the kind of wheat and the milling process.  All flours are primarily starch (about 60%) and protein (8-14%).  Compared with many other foods, flour  has very little moisture (less than 15%).  It contains small amounts of fat (from the germ) and potentially some fiber (from the bran if  it’s whole grain). Hard wheat flour is high in protein, so it’s capable of forming a sponge-like matrix when water is added and the mixture is kneaded.  Soft wheat flour is low in protein and cannot form a strong structure, even with extended kneading.  Various types of flour (all-purpose, cake, etc.) are created by mixing different proportions of hard and soft wheat together. For good results, use the type of flour indicated in your recipe.

 
Source(s):
nal.usda.gov.  “Search the USDA National Nutrient Database for Standard Reference.”
extension.missouri.edu. “Using and Storing All-Purpose Flour.”
Hoseney, R.C. 1986. Principles of Cereal Science and Technology.  A general reference on cereal foods.  Am. Assn. Cereal Chem. St. Paul, MN