Stock recipes tend to involve simmering bones and/or meat with some aromatics for a few hours, then strained. The technique transforms food scraps into a flavorful ingredient for sauces, soups and stews. You should always watch out to not let it boil, or else the stock could come out cloudy. However, there’s another technique for a clear, clean-tasting broth known as blanching.
Blanching is when you drop something in boiling water briefly, usually done with vegetables to pre-cook them. You can apply the same technique to stock, by blanching the bones and meat in water before you add the aromatics and simmer. While it may seem counterintuitive to cook the meat and bones twice, the initial boil is important because it helps the proteins clump together. This will prevent any residue that can cloud the water and give the stock a muddy flavor. It’ll minimize any scum in your final stock.
The French Method. This technique involves putting bones in a pot with cold water and bringing it up to a simmer. Afterwards, pour out the water and rinse the bones.
The Chinese Method. With this method, you bring the water to a boil, then blanch the bones and meat for 10 to 15 seconds. Then, fish them out and rinse them. Afterwards, the blanched bones and the aromatics are added to fresh, cold water and then simmered to make the final stock.
Source: the Kitchn