Sources of Riesling in Oppenheim — just any wine? (5)
I believe the answer is:
rioja
'wine?' is the definition.
(Rioja is an example)
'sources of riesling in oppenheim just any' is the wordplay.
'sources of' indicates taking the first letters.
The initial letters of 'riesling in oppenheim just any' is 'RIOJA'.
(Other definitions for rioja that I've seen before include "Spanish wine type" , "Spanish red wine" , "Wine from northern Spain" , "kind of red" , "Popular Spanish wine" .)