Wine: port certainly in Hamburg (5)
I believe the answer is:
rioja
'wine' is the definition.
(I know that Rioja is a type of red wine)
'port certainly in hamburg' is the wordplay.
'port' becomes 'rio' (Rio de Janeiro is a port).
'certainly in hamburg' becomes 'ja' ('yes' in German).
'rio'+'ja'='RIOJA'
(Other definitions for rioja that I've seen before include "Spanish wine variety" , "wine region" , "Dry red wine from Spain" , "Spanish red wine" , "Spanish drink" .)