VERBS

be, taste
The sauce tasted very sour

ADV

extremely, very
a bit, quite, rather, slightly

VERBS

be, smell, taste
The milk smelled sour
go, turn
By the next day the wine had turned sour

ADV

very
a bit, rather, slightly

VERBS

be
go, grow, turn
a bit, a little, rather, slightly, somewhat
Their friendship has turned a little sour

ADV

extremely, really, very