Clean, sweet milk is an ideal food, which requires no cooking. Heating milk to 212° F. changes its properties in some way, so that it is not considered an ideal food for babies' regular diet. If it must be used, for reasons of safety, some uncooked food, such as orange juice, should also be given. This is the reason for pasteurizing milk instead of boiling it.
Heating milk in an open vessel causes some of the protein to harden into a thin "skin" on the top. This can be prevented by stirring the milk until it is cool.