Trace of cork in Merlot perhaps producing pained expression (5)
I believe the answer is:
wince
'pained expression' is the definition.
(I've seen this in another clue)
'trace of cork in merlot' is the wordplay.
'trace of' says to take the initial letters.
'in' is an insertion indicator.
'merlot' becomes 'wine' (I am not sure about this - if you are sure you should believe this answer much more).
The first letter of 'cork' is 'c'.
'c' put inside 'wine' is 'WINCE'.
'perhaps producing' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for wince that I've seen before include "Involuntary grimace of pain" , "React involuntarily from pain or embarrassment" , "Look disgusted" , "Start painfully" , "Recoil with pain" .)