These tips will keep your broth from getting cloudy.
Clear broth is a trait valued in many soups, including our phở gà. But when you're making meat broth from scratch, you may notice it becoming cloudy. This happens when proteins in the meat's juices exude into the water or slough off the meat's surface, forming clumps as they heat that rise to the surface and create a layer of scum. As the mixture boils, the clumps break apart into tiny particles that get dispersed throughout the broth and prevent light rays from passing through the liquid, which we see as cloudiness. Fortunately, there are a number of simple ways to avoid a muddy broth.
Skim, Simmer, Strain : Our preferred method involves removing most of the coagulated proteins via skimming; simmering (versus boiling) prevents any remaining clumps from breaking apart so that they can be caught by straining (use cheesecloth).
Pressure-Cook and Strain : Under pressure, the liquid is still because there is no pressure difference between the liquid and the air space above it. This means that the protein clumps stay intact and can easily be strained once the pressure is released.
Blanch First : A dunk in a pot of boiling water (followed by a quick rinse) causes the protein clumps to form in the boiling water rather than in the broth.