Question

What happens when milk is left at room temperature in summers?

Answer 1

When milk is left at room temperature in summers it creates an ideal condition of the growth of bacterium called lactobacillus which is responsible for the formation of curd.
Due to large no. of bacterium first milk become sour and then formation of curd takes place.

Answer 2

when milk is left at room temprature in symmers , it become somewhat sour and not able to drink becz the chemical reaction takes places and the nature and the identity of the milk have somewhat changed . milk contains lactic acid, which will disappear from the milk, if milk left undistured in the room during summer.