Milling & Polishing
Grain milling is essentially a process of separating the grain into its constituents, i.e. germ, bran and endosperm. It serves three main purposes: the breaking and opening of kernels, purification of endosperm and further particle size reduction. Various classes of products can be produced from milling wheat, corn, oats and other grains ranging from fine flour to semolina, grits and flakes.
The milling of wheat starts with cleaning and tempering/conditioning the grain by adding water and/or heat. The tempered grains are placed between two large metal rollers (breakers) to separate the bran, followed by sieving and partitioning into three streams:
- Coarse material: semolina
- Large particles: composed of aleurone with bran still attached to it.
- Very fine material: referred to as farina or middling, they are the basis for making flour. The middling is sent to a purifier and the retained materials are transferred back to another set of breaker rolls. The purifier middling is sieved via vibration and air is blown over to rid them of bran residues. The middling is allowed to pass several times through the rollers for more grinding and are sifted to various flour grades. The latter are combined at different ratios to form flours of various specifications.