Question

A milkman adds a very small amount of baking soda to fresh milk. Why does he shift the pH of the fresh milk from 6 to slightly alkaline?

Answer 1

The milkman shifts the pH of the fresh milk from 6 to slightly alkaline because, in an alkaline condition, milk does not set as curd easily.

Answer 2

Usually, milk is acidic, with a pH of 6. The milkman has added a very small  amount of baking soda to the milk to make it alkaline, so that it will not become sour with the formation of lactic acid. The alkaline medium prevents the milk from changing into curd. This is the reason why the milkman has shifted the pH of fresh milk from 6 to slightly alkaline.