Question

A milkman adds a very small amount of baking soda to fresh milk.

1. Why does he shift the pH of the fresh milk from 6 to slightly alkaline?
2. Why does this milk take a long time to set as curd?

Answer 1

1. The pH of milk is 6. As the pH of milk decreases, it starts to curdle. Hence, to prevent this, the milkman adds a small amount of baking soda, a base. By doing this, he increases the pH of the milk and prevents it from curdling sooner.
2. As the pH of this milk containing baking soda (a base) is slightly higher than that of the milk without baking soda, the lactic acid produced when the milk is converted into curd must first neutralise the baking soda. As a result, it takes longer for the pH of the milk to decrease. As the pH decreases, it slowly turns into curd.