A grinding process, in a grinding unit including a first shop including a first mill and a first separator, an outlet from the first mill being connected to an inlet of the first separator; a second shop including a second separator and a second mill, an outlet from the second separator being connected to an inlet of the second mill; the second separator being fed by the material coming from the first separator, wherein the first separator is operated at a tangential speed of 15 to 25 m/s and a radial speed of 3.5 to 5 m/s; and the second separator is operated at a tangential speed of 20 to 50 m/s and a radial speed of 2.5 to 4 m/s.
