1, its own flavor: yogurt contains a large number of lactic acid bacteria, after pasteurization of sour milk, itself with a sour taste.

2, yogurt expired: Mengniu Guanyi milk yogurt shelf life of 30 days, after the shelf life will become sour.

3, yogurt bloating: because of the improper storage environment or packaging damage caused by bloating, the harmful gases in the air into the cause of sour.