Most striking stuff in certain wines (6)
I believe the answer is:
tannin
'stuff in certain wines' is the definition.
(chemical in some wines)
'most striking' is the wordplay.
'most' means to remove the last letter.
'striking' becomes 'tanning' (I've seen this before).
'tanning' with its final letter taken off is 'TANNIN'.
(Other definitions for tannin that I've seen before include "Substance used in leather production" , "Plant substance used in, eg, leather-making, medicine and red wine" , "It's found in tea and wine" , "Compound used in dying also in tea" , "Compound in tea, used in dyeing and curing hides" .)