Is milk a solid because of the fats and proteins it contains?

No. Milk is not considered a solid, it is classified as a liquid. The milk fats and proteins are suspended in a high amount of water and the mixture behaves as a liquid.

Milk isn’t a solid because it contains fats and proteins that doesn’t form a fixed, rigid structure. Instead, tiny particles are dispersed throughout the milk, which allows everything move freely. The particles aren’t locked together so milk can flow and take the shape of its container - a defining feature of liquids!

Milk is made up water (87%) and nutrients (fat, protein, sugar in the form of lactose and minerals) which make up the total solids content. Milk solids are parts of the milk that remain after the water is removed.