Beer grain (4)
I believe the answer is:
malt
'beer grain' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for malt that I've seen before include "Brewing agent" , "Pre-soaked kiln-dried cereal grain" , "Dried grain used for brewing and distilling" , "Brewing material" , "Whisky ingredient" .)