A method for controlling a crop separating process of a combine harvester with a separation device that transfers crop a cleaning device having at least one sieve with adjustable opening widths driven in an oscillating manner and a fan providing air flow upon the sieves to loosen the crop located thereon, assures that substantially three different loosening phases (F, S, W) occur during the loosening of the crop. The method determines current separation curves of the crop across a width of the cleaning device at points separated from each other in a conveyance direction (FR), evaluates the separation curves, detects the loosening phase (F, S, W) present in a conveyance direction (FR) by comparing the separation curves and initiates action depending on a detected loosening phase (F, S, W) that results in optimization of the loosening on at least one section of the cleaning device.
