Question

why does milk become sour if kept for a long time?

Answer 1

The milk become sour if kept for a long time due to bacteria named lactobecillus , these bacteria converts lactose present in the milk into lactic acid which makes a milk a sour  or we can say converts it into curd.

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ROYALJATT

Answer 2

Hey there!

How milk becomes sour?
=> When we kept milk anywhere for a long time then the bacteria grow on it. The bacteria lactobecillus grow on milk if we put it for a long time. Due to this bacteria the lactose is being converted in lactic acid which is sour in taste. That's why the milk tastes sour.

Hope it helps you!