In order to improve drying of hay-composed materials, the already dried parts must be extracted from the mixture to save energy and avoid quality problems. A separation test of a mixture of leaf and stems of ryegrass and clover for hay was developed for this, using a rotary sieve with lifter flights and the vegetal material at several moisture contents. The best separation results were found for the dried state and rotation speed of 2.1 sec−1. The stems' separation efficiencies were between 74 and 96%.