5. grinding, sifting and sieving
During the milling process, which is now beginning, the grain is placed on the first roller mill, the so-called “grist mill”, where the grain is broken up. The grain passes over more roller mills and at each one it is further crushed. This grinding process is carried out with pairs of rollers that rotate against each other at different speeds. The flutes on the rollers gently break up the grain and thus partially separate the flour kernel from the husk.
After each milling cycle, the cut grain is transported by air through pipes to plansifters. Plansifters are vibrating boxes containing a number of superimposed sieves of different mesh sizes through which the material to be ground passes. In the process, the smaller parts of the flour fall to the bottom, while the coarser parts are returned to further grinding in a roller mill.
In the semolina cleaning machines, parts of the coarse meal are separated from the husk, which is present in the mixture, by air. The semolina produced is pure coarse endosperm particles. However, these could be further crushed at any time to produce grippy or smooth flours.
The products at the end of this cycle are bran (hull parts of the grain) and various types of flour, which are stored in flour silos.