Abstract: A process and apparatus is disclosed for cleaning and opening loose fiber material which is fed through a feeder to a cleaning operation to be carried away for further processing. The degree of contamination of the fiber material is concurrently scanned. Control of the cleaning procedure is performed in response to the scanned measuring results. A measuring path is provided between a fiber feeder (2) and an opening and cleaning unit (3). At the measuring path (24), there is arranged a device (300) for scanning the degree of contamination of the fiber material. A controller (41) controls cleaning unit (3) and/or take-off rolls (8, 9) of feeder (2). The control of the cleaning procedure is relatively instantaneous in accordance wit the result of a proceeding measurement of the degree of contamination of the fiber material.