Sour-tasting beer (6)
I believe the answer is:
This clue is a triple definition!
'sour' is the first definition.
(I've seen this before)
'tasting' is the second definition.
(I have seen 'Sour tasting' mean 'bitter' so perhaps 'tasting' could also mean 'bitter')
'beer' is the third definition.
(bitter is a type of beer)
(Other definitions for bitter that I've seen before include "Sarcastic (words); very cold" , "drink" , "Tart or resentful" , "Sour like some English beer" , "Acrimonious; beer" .)