Answer:
To prevent the sudden denaturation of milk enzymes
Step-by-step explanation:
The HCl is a very strong acid, with a pH of about 2. However, milk contains a component of substances in their natural state in solution. For example, lactose enzyme, the fatty emulsion, as well as the protein casein in a colloidal suspension.
In addition, the pH of the major components of milk which involve calcium are basic, or alkaline. The pH of the calcium compounds is around 6.8 - 7. This is a basic environment. Thus, because of the basic nature of the milk, it has a buffering effect on the acid.
When HCl is added to the milk, the casein molecules are affected. So, adding HCl slowly is necessary to prevent the denaturation of the casein molecules.