Collocations for sour - adj.

be, taste
The sauce tasted very sour.

extremely, very | a bit, quite, rather, slightly

be, smell, taste
The milk smelled sour.

go, turn
By the next day the wine had turned sour.

very | a bit, rather, slightly

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

extremely, really, very