Grain as used for brewing drink (7)
I believe the answer is:
sangria
'drink' is the definition.
(type of alcoholic drink)
'grain as used' is the wordplay.
'used' indicates anagramming the letters.
'grain'+'as'='grainas'
'grainas' is an anagram of 'SANGRIA'.
'for brewing' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for sangria that I've seen before include "Mixed drink" , "Spanish wine cocktail" , "Spanish alcoholic drink" , "Spanish drink of red wine, sugar and fruit" , "Spanish spiced wine" .)