Milk fat is mostly found in the form of a globule. The large globules in raw and unhomogenised milk have a lower density than much of the material in milk and will rise to the surface. This phenomenon is known as creaming. The casein in homogenised milk interacts with the broken-up milk fat globules and prevents them from coalescing, keeping the milk in a more even emulsion.
Lactose is a disaccharide, made up of galactose and glucose bonded together. Lactose is 70% less sweet than sucrose.