Decisive point in wine classification vote (4)
I believe the answer is:
crux
'decisive point' is the definition.
(I've seen this before)
'wine classification vote' is the wordplay.
'wine classification' becomes 'cru' (I can't justify this - if you can you should believe this answer much more).
'vote' becomes 'x' (how votes are marked).
'cru'+'x'='CRUX'
'in' is the link.
Can you help me to learn more?
(Other definitions for crux that I've seen before include "Decisive point of an issue" , "Core" , "Nub" , "Essential point of problem, decision etc" , "Most important point at issue" .)