Cereal husks (5)
'cereal husks' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for bran that I've seen before include "Food for horses in barn" , "Healthy breakfast" , "Husks of cereal seeds sifted from flour" , "Element in high fibre diet" , "Refuse from grain" .)
(Other definitions for chaff that I've seen before include "Refuse - banter" , "Laugh at" , "Husks - jokes" , "shells" , "twit" .)