spent grain vs brewer's grain

spent grain and brewer's grain both are nouns.

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

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

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

Other synonyms of spent grain include draff.

spent grain (noun)	brewer's 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.