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
