Yellowish-brown grain is a perfume ingredient (9)
I believe the answer is:
ambergris
'a perfume ingredient' is the definition.
(I've seen this before)
'yellowish-brown grain is' is the wordplay.
'yellowish-brown' becomes 'amber' (I've seen this in another clue).
'grain' becomes 'gr' (short for grain, a unit of mass).
'amber'+'gr'+'is'='AMBERGRIS'
(Other definitions for ambergris that I've seen before include "Sperm whale secretion used in perfume manufacture" , "Perfume ingredient from whales" , "Wax-like substance" , "part of whale" , "Sperm whale secretion used in perfumes" .)