Wheat is harvested by combines that cut the stalk remove and collect the seed, and either return the straw to the soil, to be plowed under with the stubble and thus provide hummus or compress and bale it for future use as litter, ensilage and so on.
Wheat may be bagged in jute sack and stored in warehouses or it may be stored in bulk in elevators. The latter method provides the best protection against rodent and insect infestation.The moisture content of bulk stored wheat should not be higher than 14.5% and that of sack stored wheat not higher than 16%. Otherwise, microorganism may grow and cause heating and spoilage. When it is necessary to lower the moisture content of wheat it may be dried in bins by blowing hot air (not higher in temperature than 175 degree F) across the bins.
In preparing wheat for milling, it is blown into hopper scales that record the quantity of uncleaned wheat. Some of the coarser impurities are removed by this process. The grain then passes over a series of coarse and fine sleeves that further remove contaminating materials, including chaff and straw. Still in dry states stones may be removed by passing wheat over short openings that allow the heavier stones to fall out of mass and be trapped.
The wheat is next passed over discs or cylinders containing indented surface that remove seeds short or longer than wheat following a pass through a magnetic separator to remove any metals present. The next cleaning process is dry scouring to remove adhering dirt.
The wheat is then washed in water, a process that both removes dirt and adds 2 – 3% water to the grain. The added water is necessary to provide desirable conditions for milling. A stone trap is including in the washer. Excess water is removed by centrifugation. A second wet cleaning with a light brushing action is ordinarily used, followed by aspiration (blowing air through the grain), which is the final cleaning operation.
The grain is then carried into a bin from which it is fed to the milling operation. This bin is located on the top floor of the flour mill, the grain having been elevate do this position during the various cleaning operation.
In milling, grain is fed automatically though scale hoppers that regulate the flow of the seeds at rates corresponding to those of the following operations:
Milling may be carried out by passing the grain through a series of corrugated rolls rotating toward each other, which remove chunks of the endosperm from the bran. After each passage through the break rolls, the material is sifted through cloth, or wire sieve and separated according to particle size.
The various streams of different sized flour particles are finally blended to provide the different grades of flour. The more finely ground flour is nearer to white but less nutritious than the coarser ground flour.
This results from the more effective removal of bran and germ from finely ground flour. Impact milling is now used in some operations. With this method, the seed is broken open by impact in a machine. Flour particles of different sizes are separated by air classification or by centrifugation.
Wheat Grain Processing
