Milk contains some molecular substances which make themilk come to the surface when it is boiled
whereas water does not contain such substances but water does reduces soon for boiling more than 10min but milk takes a half day to reduce
Milk is a colloidal substance .we can observe tyndall effect in milk . due to that the  size of milk increases and it will come out from beaker .
water doesn't have such resources .so on boiling water the water doesn't com out and the quantity of water reduces .milk takes nearly 1 hr to boil and quantity become less .