Knock back some elderberry wine (3)
I believe the answer is:
Here is my best explanation:
'wine' is the definition.
(red wine is a kind of wine)
'knock back some elderberry' is the wordplay.
'knock back' says the letters should be written in reverse.
'some' indicates a hidden word (some of the parts of the word are used).
'der' is hidden within 'elderberry'.
'der' in reverse letter order is 'RED'.
(Other definitions for red that I've seen before include "Merchant flag", "Cardinal, for example", "Carmine", "Blood-coloured", "Bordeaux claret, for instance", "socialist?", "Cardinal's colour", "lefty", "Ruby" and "Florid".)