"sour milk"

"a false (or sour) note"
"her singing was off key"

"a dark scowl"
"the proverbially dour New England Puritan"
"a glum, hopeless shrug"
"he sat in moody silence"
"a morose and unsociable manner"
"a saturnine, almost misanthropic young genius"
"a sour temper"
"a sullen crowd"

"The milk has soured"
"The wine worked"
"The cream has turned--we have to throw it out"