Classifier and method for operating a classifier

The invention discloses a classifier and a method for operating a classifier. The method according to the invention for operating a classifier for classifying piece-form material has the following method steps: a rotary cage is rotated, classifying air is taken, through an air-routing system enclosing the rotary cage, into a classifying zone formed between the rotary cage and air-routing system, and the piece-form material is supplied into the classifying zone, wherein one or more inserts are arranged in the classifying zone such that the torque to which the rotary cage is subjected at the same rotational speed is increased by at least 20% in relation to a design without any inserts and/or the distance between the air-routing system and the rotary cage is selected such that the torque to which the rotary cage is subjected at the same rotational speed is increased by at least 20% in relation to a design in which the air-routing system is at a distance which does not affect the torque of the rotary cage.