Head off or drop content of American brew (3,2,3,3)
I believe the answer is:
nip in the bud
If this is the answer I cannot explain how the clue works.
Can you help me to learn more?
(Other definitions for nip in the bud that I've seen before include "close early" , "Put an end to something in initial stages" , "Prevent before growth occurs" , "stop early on" , "evidence of springtime frost?" .)