When braising pork in dishes like Tau Yu Bak, you may notice foam or scum rising to the surface of the cooking liquid. This is caused by proteins and impurities being released from the meat as it cooks. To remove the scums, use a spoon or a fine mesh skimmer to skim off the foam and scum that rises to the top, This helps to remove impurities from the cooking liquid and results in a clearer and cleaner broth.