Brewery grain (4)
I believe the answer is:
malt
'brewery grain' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for malt that I've seen before include "Germinated and kiln-dried grain used in brewing and distilling" , "Pure whisky" , "Whisky ingredient" , "Kind of Scotch whisky" , "Grain product used in beer and whisky" .)