during its passage from the end of the conveyor 2 to the receptacle 10 the material is kept in the product stream a solely by its own momentum ejectors 12 extend over the width of the product stream and are operable to remove items from specific zones of the product stream 8 by high pressure air jets directed towards the reject receptacle 14 typically the width of the product stream is around 500 mm with forty ejectors equally spaced thereover the ejectors are instructed by a computer or a microprocessor 16 which itself receives input data from the optical scanning system 18 described below reference 20 indicates a viewing station where product in the product stream 8 is scanned the station is illuminated by visible light on one side from the sources 22 and with radiation from a further source 24 on the other side the source 24 can be of visible light but may alternatively be of light in the infra red range as will be described below light reflected from product in the product stream as it passes through the viewing station 20 is monitored by an array of sensors 26 in the form of charge coupled devices ccds sensitive to light in different wavelengths in its passage to the sensors 26 the light is split into discrete beams at a prism section 28 and the resultant three beams are filtered to restrict the transmitted light to the appropriate.