Separate the wheat from the chaff (6)
I believe the answer is:
thresh
'separate the wheat from the chaff' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for thresh that I've seen before include "Beat seeds out of grain" , "Beat (stalks to get grain)" , "Separate corn from husks by beating" , "Extract grain (with flail)" , "Beat grain or make violent movements" .)