A counterflow single-screw extractor includes a screw conveyor having a helical scroll formed from arcuate flight sections each having a plurality of elongated slots extending away from the direction of screw rotation and permitting the flow of effluent through the product and the flights in a manner controlled by the size, number, and orientation of the slots. The slots permit efficient extraction using relatively little extraction medium and at the same time permit a single-screw extractor to be used without having to periodically reverse the direction of screw rotation to unclog the slots and by the pitch of the screw conveyor. The inventive arrangement permits the use of a multi-section extractor employing different extraction media and/or different extraction media wash rates in different sections of the extractor.