Subsurface Scattering can be used in a variety of ways. One of them is when you need to create a semi-translucent material like milk.
the basic principles of transparency, refraction and the Sub Surface Scattering shader.
Here, CyBear posts a look into creating the difficult material of milk. A lot of the process of how the scene looks is generated from the scene’s lighting itself.
Milk, looks like it does because of the larger fat droplets and smaller casein micelles which are just large enough to deflect light. Both of them contribute to the opaque white color of the milk.
This can be simulated in CG by using a Subsurface Scattering effect where the light will make its way through the surface of a material instead of bouncing off.