Somewhat disheartened by a single wine (4)
I believe the answer is:
asti
'wine' is the definition.
(I've seen this before)
'somewhat disheartened by a single' is the wordplay.
'disheartened' means to remove the middle letters.
'by' says to put letters next to each other.
'single' becomes 'i' (one).
'somewhat' with its centre taken out is 'st'.
'st' after 'a' is 'ast'.
'ast'+'i'='ASTI'
(Other definitions for asti that I've seen before include "It's a (anag) - wine" , "Sparkling wine named after an Italian Piedmont town" , "Piedmont wine city, SE of Turin" , "Source of fizz" , "Capital of a north-west Italian province, known for its sparking wine" .)