Why does milk curdle? Milk curdle because of bacteria present in the milk

Why does milk curdle? Milk curdle because of bacteria present in the milk

Why does milk curdle? Generally when a sour substance touches the milk it curdles. Some time even without mixing anything milk curdles. There are some bacteria which are harmful as well as some bacteria which are helpful to us. Milk contains the bacteria which is harmless. These bacteria used the Lactose present in the milk for reproduction. During this process, Lactose becomes Lactic acid. When milk is stored for a long time, Lactic acid is developed in the milk and the milk becomes sour and curdles. Which means when the milk is stored for a long time bacteria in the milk becomes harmful.