Wine producer conceals a fast message (9)
I believe the answer is:
valentine
'message' is the definition.
(I know that Valentine is a type of correspondence)
'wine producer conceals a fast' is the wordplay.
'wine producer' becomes 'vine'.
'conceals' is an insertion indicator.
'fast' becomes 'lent' (Lent is a period of fasting in Christianity).
'a'+'lent'='alent'
'vine' going around 'alent' is 'VALENTINE'.
(Other definitions for valentine that I've seen before include "Saint regarded as the patron of lovers" , "Anonymous love token from an admirer" , "Card to sweetheart" , "A loving greeting card sent on February 14th" , "Potential lover" .)