Brewer's grain (4)
I believe the answer is:
malt
'brewer's 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" , "Barley product used in brewing" , "Cereal grain for distilling" , "strong drink" , "Pre-soaked kiln-dried cereal grain" .)