While digesting milk,it mixes with HCL acid, what happens at that moment when they get mixed or what will happen if we mix HCl with milk.
In natural state the major components in milk are present in different states: lactose in solution( in water of milk), fat in emulsion ( as globules), major protein casein is in colloidal suspension.
Among these components ( along with Calcium) remain stable at normal pH ( around 6.8) of milk.
Milk has also some buffering capacity.
When hydrochloric acid HCl) added to milk, the pH drops below milk’s normal pH in which the stability of casein molecules will be most affected ( beyond the buffering level). The molecules will go through some form of denaturation, forming soft gel at low HCl level and then coagulating and separating out from the watery portion.