How is the soup stewed with fish in iron pot cooked?

Raw material formula of stewed fish in iron pot;

2 old hens, 3kg of pork bones, 2kg of ribs, duck feet 1kg, and seasoning packages (20g of star anise, 25g of pepper, 30g of cinnamon, 35g of galangal, 20g of dried tangerine peel, 30g of licorice 15g of fragrant leaves, 30 g of tsaoko 15g of angelica dahurica).

Making:

Blanch these raw materials respectively, put them into a soup bucket, add 20kg of clear water, boil them with strong fire, skim off floating powder, turn to low fire and cook for 4hr, then take out the raw materials for hanging soup, and add salt 120g, soy sauce 200g, balsamic vinegar 100g, dried pepper 20g and monosodium glutamate 75g.