Milk is the product secreted from the mammary glands of mammals, intended for the feeding of young newborn animals.
From a physical and chemical point of view, milk is a very complex product made up of :
A mixture of solubilised liquid or solid substances, called solutes, in a liquid solvent.
This is a mixture consisting of a non-solubilised solid dispersed phase, present as very fine solid particles in a liquid dispersing phase. When the particles have a high affinity with the aqueous phase, this system is called a colloidal solution.
This is a mixture of a non-solubilised liquid dispersed phase, present as very fine droplets, in a liquid dispersing phase. We can therefore have an oil-in-water (O/W) emulsion or a water-in-oil (W/O) emulsion. The fat and water in the milk form an O/W emulsion.