Why do I need to add vinegar? The apple cider vinegar added in the beginning of the recipe helps leach the nutrients out of the bones and into the broth.
How hard should I boil it? A rolling boil is not recommended. Bring the pot to an initial boil and turn the heat down to a gentle simmer. To much boiling will break down the collagen in the bones or chicken feet. A gentle simmer will help bring the collagen into the broth.
A really good stock will turn gelatinous when chilled. It your cooled broth has become one solid lump after a night in the fridge, you have done a good job. No worries, the broth will promptly liquify again with just a little warmth.
Chicken Noodle Soup: Add diced carrots, celery, cooked diced chicken meat and noodles to 2-3 quarts of homemade chicken stock.
Stock Cubes: pour cooled stock into an ice cube tray and freeze. Store cubes in zip lock bag in freezer and use when ever you need a few tablespoons of stock.