draff vs flotsam

draff

noun
  • A byproduct from a grain distillery, often fed to pigs or cattle as part of their ration; often synonymous with brewer's spent grain, sometimes differentiated from it; usually differentiated from potale, at least in technical use, although broad, nontechnical use has often lumped all such byproducts together, especially in the past. 

flotsam

noun
  • Debris floating in a river or sea, in particular fragments from a shipwreck. 

How often have the words draff and flotsam occurred in a corpus of books? (source: Google Ngram Viewer )