Grain processing: Pearling process

The principal procedure of cereal processing is milling—that is, the grinding of the grain so that it can be easily cooked and rendered into an attractive foodstuff.

Milling is classified in two categories: dry and wet, while each has its own characteristics. Dry milling separates the outer fibrous materials and germ, which are considered by-products of the grain endosperm.

Debranning is increasingly recognized by the milling and baking industry as an important stage in cereal processing because it lowers the capital investment costs, giving as well, the benefit of better-quality products. Debranning is a treatment usually used in rice but has been adapted for wheat. It is controlled process where the outer grain layers are removed. There are two types of debranning either by friction which is also called peeling or abrasion that is called pearling.

Dry milling can also refer to pearling. This may be done by abrading it off between grindstones. Pearling is done by rubbing the grains against abrasive stones and air pressure is used to remove the pearling. This process will remove up to 18% of the grain which could correspond to a removal of the entire bran. The application of abrasion and friction removes effectively only the bran layers from the cereal grains (rice, oat and barley), allowing nutritious parts, such as the aleurone layer to remain in the intact kernels. This pre-treatment potentially could also improve milling yields of superior flour quality.

The advantage that pearled grain has over whole grain is that it cooks faster. It is also quite tender. Pearled grain is also known as polished grain.

The by-products of the pearling process, ≈30–40% of the total kernel weight, are mainly used in animal feed. These by-products contain interesting amounts of bioactive compounds such as β glucans, tocopherols, and tocotrienols.
Grain processing: Pearling process

Oats processing: Cleaning

As with numerous agricultural products, harvesting oats will lead to co-mingling of the oats with other components found in the field and transportation process, and these foreign materials need to be removed to make oats suitable for human consumption.

Cleaning removes the unwanted materials – such as corn, soybeans, foreign material, weed seeds, wheat, or barley – from the milling quality oats.

The oats are brought at harvest into the mill by the growers. The miller only accepts oats that will yield flakes of satisfactory quality, and will attempt to maximise profits by estimating the potential yield and looking at the price of the oats and any possible added value obtainable. The oats then cleaned and dried so that they may be safely stored until they are needed. When the oats enter the mill, they pass under a magnetic separator to remove foreign metal objects, a very common practice in many food-processing operations.

The they are cleaned, taking off straws, stones and weed seeds and are then sent through a stream of air to remove any dust or light grains that would be unsuitable for milling.

This is followed by a dry stoner that removes high-density but similar-sized particles such as rocks and other grains, such as maize.

Even high quality oat grain will require cleaning to ensure that only sound oats are processed. The oats must appear wholesome and clean, must be free from extraneous material, with large and light coloured oats that give a high yield being preferred.

Oats processing: Cleaning   

Grain processing: cleaning

Grain cleaning reduces the problems that occur during storage and handling. Clean grains save storage space and increase marketability.

Over the years there has been rapid development of machinery for grain cleaning. The one most often used employ the air screen system, which was the basis for the oldest cleaning machines and still is the easiest and most effective form of cleaning bulk grain.

The mill is the point where cereals are transformed from agricultural commodities to foods or food ingredients.

Physical cleaning takes place in the mill to remove straw and chaff, stones, soil and metal fragments, which could damage the mill, damaged or ergot-infected grains, seed other than the cereal grain required, insects and other foreign matter.

In preparing wheat cleaning, the wheat 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 passed over a series of coarse and fine sieves that further remove contaminating materials, including chaff and straw.

The various dry cleaning processed used in modern four mills have little effect on the microbiological condition of the grain.

The efficiency of the cleaning operation is dependent on the efficiency of the machine, the selection of appropriate screens for the particular task and the competence of the operator.
Grain processing: cleaning