spent grain vs draff

spent grain and draff both are nouns.

Word	Noun	Adjective	Verb	Adverb
spent grain	Yes	No	No	No
draff	Yes	No	No	No

As nouns, spent grain and draff are synonyms defined as:

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

Other synonyms of spent grain include brewer's grain.

spent grain (noun)	draff (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.