brewer's grain vs spent grain

brewer's grain and spent grain both are nouns.

Word	Noun	Adjective	Verb	Adverb
brewer's grain	Yes	No	No	No
spent grain	Yes	No	No	No

As nouns, brewer's grain and spent grain are synonyms defined as:

brewer's grain and spent grain: the residue of malt and grain which remains in the mash-kettle after the mashing and lautering process.

Other synonyms of brewer's grain include draff.

brewer's grain (noun)	spent grain (noun)
the residue of malt and grain which remains in the mash-kettle after the mashing and lautering process.	the residue of malt and grain which remains in the mash-kettle after the mashing and lautering process.