The Zig-zag sifter separates the feed material mixture into coarse and fine fractions. Classification takes place in multiple stages at the kinks in the zigzag channel, where coarse material is separated from fine material. A continuous, rising airflow operates within the channel. As the material moves over the kinks in the classifier walls, the lighter fraction is caught by the airflow and transported upwards to the extraction point. The heavier fraction falls downwards and is removed.