German's fine after port wine (5)
I believe the answer is:
rioja
'wine' is the definition.
(I know that Rioja is a type of red wine)
'german's fine after port' is the wordplay.
'german's fine' becomes 'ja' ('yes' or 'fine' in German).
'after' means one lot of letters go next to another.
'port' becomes 'rio' (Rio de Janeiro is a port).
'ja' after 'rio' is 'RIOJA'.
(Other definitions for rioja that I've seen before include "it comes from grapevine" , "Wine from northern Spain" , "Open space (ancient Greek)" , "kind of red" , "Spanish wine type" .)