Plastic bags covering up a bit of brewer’s droop (3)
I believe the answer is:
sag
'droop' is the definition.
(synonyms)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for sag that I've seen before include "Spinach as used in Indian cookery" , "Droop, flag" , "Cave in" , "Give way under pressure" , "Sink, hang down" .)