Unpleasant quality of wine going to the head after end of luncheon (9)
I believe the answer is:
nastiness
'unpleasant quality' is the definition.
'wine going to the head after end of luncheon' is the wordplay.
'wine going' becomes 'asti' (I can't explain this - if you can you should give a lot more credence to this answer).
'to the head' becomes 'ness' (ness is a headland).
'after' says to put letters next to each other.
'end of' suggests the final letters.
The last letter of 'luncheon' is 'n'.
'asti'+'ness'='astiness'
'astiness' after 'n' is 'NASTINESS'.
'of' is the link.
Can you help me to learn more?
(Other definitions for nastiness that I've seen before include "ill humour" , "Malevolence" , "hostility" , "Unpleasant behaviour" , "Repugnant behaviour" .)