Great kipper knocking out a cold gourmet (7)
I believe the answer is:
Here is my best explanation:
'gourmet' is the definition.
('epicure' can be a synonym of 'gourmet')
'great kipper knocking' is the subsidiary indication.
'great' becomes 'epic'.
'kipper knocking' becomes 'ure' (I can't explain this - if you can you should believe this answer much more).
'out a cold' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
(Other definitions for epicure that I've seen before include "Bon vivant", "One enjoying fine food and drink", "The gourmet", "discriminating person", "Lover of fine food and drink", "anything but a John the Baptist type?", "Gourmet", "Person with refined tastes in food and drink", "Person with fastidious tase in food and wine" and "Person with refined taste in food and drink".)