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

Why does this milk take a long time to set as curd?

• The pH value of milk is $6$ at i.e. it is mildly acidic in nature.
• Due to the action of bacteria, the milk is converted into curd as a result, lactic acid is formed which is more acidic in nature.
• By adding Baking soda or Sodium bicarbonate $\left({\mathrm{NaHCO}}_3\right)$, the pH of the milk turns slightly alkaline.
• A long time is required for the milk to set into curd as the lactic acid produced here first neutralizes the pH and then the pH is reduced to turn the milk into curd.
• Hence, this milk takes a long time to set into the curd.