Discover the differences between milling and grinding

Various operations are required for the preparation of powders. One of these operations is to convert larger grains into smaller particles. The industry uses various types of machines for this. The two English terms milling and grinding are common in these types of operations and are often used interchangeably.

Milling is equivalent to grinding and originally is the process of converting granular materials into smaller pieces by means of compressive force. Examples are the conversion of grain into flour and the transformation of peppercorns into pepper powder. This was done by pulverizing granules on an annular surface, by means of heavy revolving stone wheels. Initially, the stones were driven with the help of horses that supplied the energy for this in a treadmill. Soon there were windmills and watermills that powered the pumping station.

Grinding stands for crushing and, like milling, involves the conversion of grains into smaller pieces or powder. Unlike milling, no compressive forces are used, but shear forces in combination with compressive force. In grinding, the grains are located in a narrow annular opening. At the inlet, where the grains enter the grinding mechanism, the annular opening is so large that the grains fit in completely. The annular opening narrows downwards. Both the inner and outer wall are provided with grooves that exert resistance to the grains. As soon as the inner wall of the opening starts to rotate, the grains in the opening set in motion and are thereby subjected to shearing. This will break the grains into smaller pieces. The broken pieces sink further and further and are broken again and again. Examples of this mechanism are a traditional coffee grinder or a pepper grinder.