2. soak the bought pig bones in water for half an hour to soak the blood out.
3. Boil the water, add the bones and add a little cooking wine. Boil the water for about 5 minutes, take out and rinse the foam for later use.
4. Change the water and boil it again, then add the bones, add the appropriate amount of vegetable oil, a little onion, ginger and garlic, and simmer slowly. Note that adding bones to the water after boiling can make the soup clearer and more milky.
5. When stewing the bone, peel and cut the yam into sections and soak it in water to prevent oxidation. You can add a little white vinegar to the water appropriately, and the effect is better.
6. Stew the pork bones in a pressure cooker for 30-40 minutes. If you use a casserole, it will take about 1 hour. You can smell bones. After the flesh and blood are separated, put the yam into the pot.
7. Add a little salt and chicken essence, then simmer 10- 15 minutes.