Port? Yes, foreign wine (5)
I believe the answer is:
rioja
'foreign wine' is the definition.
'rioja' can be an answer for 'wine' (Rioja is an example). I am not certain of the 'foreign' bit.
'port? yes' is the wordplay.
'port?' becomes 'rio' (Rio de Janeiro is a port).
'yes' becomes 'ja' (I can't justify this - if you can you should believe this answer much more).
'rio'+'ja'='RIOJA'
Can you help me to learn more?
(Other definitions for rioja that I've seen before include "Open space (ancient Greek)" , "North Spanish wine" , "wine region" , "Spanish wine variety" , "Spanish table wine" .)