Rendered tune backwards after drink (7)
I believe the answer is:
sangria
'drink' is the definition.
(sangria is a kind of drink)
'rendered tune backwards after' is the wordplay.
'rendered' becomes 'sang' (singing is a kind of rendering).
'tune' becomes 'air' (I've seen this before).
'backwards' says the letters should be written backwards.
'after' is a charade indicator (letters next to each other).
'air' reversed gives 'ria'.
'sang'+'ria'='SANGRIA'
(Other definitions for sangria that I've seen before include "Mixed drink" , "Spanish wine/fruit drink" , "Red wine, fruit juice, sugar and spices" , "Spanish wine punch" , "Spanish drink of red wine, sugar and fruit" .)