I use only the skin and boned carcass for the broth. It is the collagen, as described in above posts, that causes the gelling. The collagen is found in connective tissues, bone joints, and in the marrow. It is recommended that the pones be cracked to extract the valuable nutrients from inside. The combination of collagen, and inner bone nutrients from the marrow add both flavor and nutritional value to the soup. Also, the addition of slightly acidic veggies such as celery root will aid in the extraction of the collagen and marrow.
When the broth is made, strain it and refrgerate overnight. The next day, lift the hard layer of fat from the top. Bring to a simmer and add the other veggies. Cube, then cook the meat last, seperate, in a bit of sunflower oil, and lightly salted until just lightly browned. Add the meat to the soup bowls. This truly produces a superior soup with high nutritional value. And it is good in building up the body against vilar and bacterial infections.
Oh, and flavor the broth with salt, pepper, sage, thyme, etc. prior to adding the other veggies. Then, after the veggies are done to your liking, correct the seasoning again.
Seeeeeya; Goodweed of the North