Tasting sour (6)
I believe the answer is:
rancid
'tasting sour' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for rancid that I've seen before include "Like fat that's gone off" , "(Of butter) gone off" , "Smelling bad like stale fat" , "Fragmented bricks etc." , "Smelling or tasting bad" .)