Does this sound natural?
“The milk is so sour. I believe it’s gone sour.”

查看翻譯

the milk goes bad: implies the present tense, or whatever it's called.
example: every time you leave the fridge open, the milk goes bad.

the milk HAS gone bad: it's in the past... it's expired... it's sour (don't drink it
(or: the milk's gone bad. same thing)
example: "honey the milk's gone bad. please get some more at the store"