General information about flour:
From Wikipedia: “Flour is a powder made by grinding uncooked cereal grains or other seeds or roots (like cassava). It is the main ingredient of bread, which is a staple food for many cultures, making the availability of adequate supplies of flour a major economic and political issue at various times throughout history. ...
While wheat is the most common base for flour, maize flour has been important in Mesoamerican cuisine since ancient times and remains a staple in the Americas. Rye flour is a constituent of bread in central Europe.”
“In some markets, the different available flour varieties are labeled according to the ash mass that remains after a sample is incinerated in a laboratory oven. ...
German flour type numbers (Mehltypen) indicate the amount of ash (measured in milligrams) obtained from 100 g of the dry mass of this flour. Standard wheat flours (defined in DIN 10355) range from type 405 for normal white wheat flour for baking, to strong bread flour types 550, 812, and the darker types 1050 and 1600 for wholegrain breads.”
“Flour contains a high proportion of starches, which are a subset of complex carbohydrates also known as polysaccharides. The kinds of flour used in cooking include all-purpose flour (known as plain outside North America), self-rising flour (known as self-raising outside North America), and cake flour including bleached flour. The higher the protein content the harder and stronger the flour, and the more it will produce crusty or chewy breads. The lower the protein the softer the flour, which is better for cakes, cookies, and pie crusts.”
Flour should be stored at temperatures below 20°C and a relative humidity of below 65%. White flours (up to approx. type 812) can then be stored for 1 to 1½ years, darker flours (up to type 1050 or 1370) for six to eight months, and whole grain products for about six to eight weeks without any loss of quality. If the storage period is longer ... the flour begins to spoil.
Degermed and heat-processed flour:
“An important problem of the industrial revolution was the preservation of flour. Transportation distances and a relatively slow distribution system collided with natural shelf life. The reason for the limited shelf life is the fatty acids of the germ, which react from the moment they are exposed to oxygen. This occurs when grain is milled; the fatty acids oxidize and flour starts to become rancid. Depending on climate and grain quality, this process takes six to nine months. In the late 19th century, this process was too short for an industrial production and distribution cycle. As vitamins, micronutrients and amino acids were completely or relatively unknown in the late 19th century, removing the germ was an effective solution. Without the germ, flour cannot become rancid. Degermed flour became standard. Degermation started in densely populated areas and took approximately one generation to reach the countryside. Heat-processed flour is flour where the germ is first separated from the endosperm and bran, then processed with steam, dry heat or microwave and blended into flour again.
The FDA has been advised by several cookie dough manufacturers that they have implemented the use of heat-treated flour for their "ready-to-bake cookie dough" products to reduce the risk of E. coli bacterial contamination.”
“Milling of flour is accomplished by grinding grain between stones or steel wheels. Today, "stone-ground" usually means that the grain has been ground in a mill in which a revolving stone wheel turns over a stationary stone wheel, vertically or horizontally with the grain in between. ...
Home users have begun grinding their own flour to from organic wheat berries on a variety of electric flour mills. The grinding process is not much different from grinding coffee but the mills are much larger. This provides fresh flour with the benefits of wheat germ and fiber without spoilage.”
“Flour dust suspended in air is explosive—as is any mixture of a finely powdered flammable substance with air (see dust explosion). Some devastating explosions have occurred at flour mills, including an explosion in 1878 at the Washburn "A" Mill in Minneapoliswhich killed 22 people.”