Source of grapes, fish and sour-tasting liquid (7)
I believe the answer is:
vinegar
'sour-tasting liquid' is the definition.
(vinegar tastes sour)
'source of grapes fish' is the wordplay.
'source of grapes' becomes 'vine' (grapevine).
'fish' becomes 'gar' (gar is a kind of fish).
'vine'+'gar'='VINEGAR'
'and' is the link.
(Other definitions for vinegar that I've seen before include "Sour liquid used as condiment" , "Sourish liquid for flavouring chips" , "Peevishness" , "Pickling agent" , "Pickling fluid" .)