Translation guide
Describes when a situation, relationship, or mood becomes bad, unpleasant, or hostile. Also used literally for food or milk going bad.
The learner wants to say that a previously good or neutral situation, plan, deal, or relationship has become unpleasant, hostile, or unsuccessful.
The most general and natural way to say something 'turns bad'. Works for relationships, situations, weather, etc.
Their relationship suddenly turned sour.
The negotiations are turning sour.
Specifically for relationships or situations that become tangled, complicated, and worse. Often used for romantic relationships or negotiations.
The discussion turned sour (became complicated and hostile).
Describes an atmosphere or relationship becoming tense, hostile, or strained. Stronger than 悪くなる.
The atmosphere of the meeting turned sour.
Literally 'become bad-tasting', but can metaphorically mean a situation turns sour or goes wrong. Casual.
The conversation turned sour.
The learner wants to describe a person's mood, expression, or attitude turning sour, i.e., becoming displeased, sullen, or hostile.
The standard way to say someone's mood turns sour or they become displeased/grumpy.
He suddenly turned sour.
Her expression turned sour.
To sulk or become sullen, often in a childish way. Describes a quick mood change to sourness.
To put on a sour face, look sullen. Literally 'Buddha-top face', meaning a grim expression.
He had a sour face all day.
The learner wants to say that food, especially milk, has spoiled or gone sour.
General verb for food going bad, rotting. Covers 'turn sour' for milk and other spoilage.
The milk turned sour.
Specifically means 'become sour' in taste. Used for milk, wine, etc. when the sourness is the main point.
The milk turned sour.
Food goes bad, spoils. More common for perishables like vegetables, fruit, or cooked food.
Do not translate 'turn sour' literally as 酸っぱくなる for situations or moods. That would mean the situation became sour-tasting, which is unnatural. Use 悪くなる or 不機嫌になる instead.
The relationship turned sour. (Incorrect, sounds like it became sour-tasting)
ちょっと注意したら、すぐむくれた。
When I gave him a little warning, he immediately turned sour.
This meat has gone bad.
暑さで食べ物が傷んだ。
The food turned sour in the heat.