General process information
Wheat is received at the flour mill and inspected. The wheat is stored in silos with wheat of the same grade until needed for milling.
Before wheat can be ground into flour it must be free of foreign matter. This requires several different cleaning processes. At each step of purification the wheat is inspected and purified again if necessary.
The first device used to purify wheat is known as a separator. This remove large objects such as sticks and rocks.
The wheat next passes through an aspirator. The aspirator sucks up foreign matter which is lighter than the wheat and removes it.
Other foreign objects are removed in various ways.
The purified wheat is washed in warm water and placed in a centrifuge to be spun dry. During this process any remaining foreign matter is washed away.
The moisture content of the wheat must now be controlled to allow the outer layer of bran to be removed efficiently during grinding. This process is known as conditioning or tempering.
Cold conditioning involves soaking the wheat in cold water for one to three days. Warm conditioning involves soaking the wheat in water at a temperature of 115°F (46°C) for 60-90 minutes and letting it rest for one day. Hot conditioning involves soaking the wheat in water at a temperature of 140°F (60°C) for a short period of time. If conditioning results in too much moisture, or if the wheat happens to be too moist after purification, water can be removed by vacuum dryers.
Wheat of different grades and moistures is blended together to obtain a batch of wheat with the characteristics necessary to make the kind of flour being manufactured. At this point, the wheat may be processed in an Entoleter, a trade name for a device with rapidly spinning disks which hurl the grains of wheat against small metal pins. Those grains which crack are considered to be unsuitable for grinding and are removed.
The wheat moves between two large metal rollers known as breaker rolls. These rollers are of two different sizes and move at different speeds. They also contain spiral grooves which crack open the grains of wheat and begin to separate the interior of the wheat from the outer layer of bran. The product of the breaker rolls passes through metal sieves to separate it into three categories. The finest material resembles a coarse flour and is known as Endosperm. Larger pieces of the interior are known as germs. The third category consists of the bran. The Endosperm move to the Endosperm purifier and the other materials move to another pair of breaker rolls. About four or five pairs of breaker rolls are needed to produce the necessary amount of Endosperm.
The Endosperm purifier moves the Endosperm over a vibrating screen. Air is blown up through the screen to remove the lighter pieces of bran which are mixed with the Endosperm. The Endosperm pass through the screen to be more finely ground.
Endosperm are ground into flour by pairs of large, smooth metal rollers. Each time the flour is ground it passes through sieves to separate it into flours of different fineness. By sifting, separating, and regrinding the flour, several different grades of flour are produced at the same time. These are combined as needed to produce the desired final products.
Small amounts of bleaching agents and oxidizing agents are usually added to the flour after milling. Vitamins and minerals are added as required by law to produce enriched flour. Leavening agents and salt are added to produce self-rising flour. The flour is matured for one or two months.