I recently cooked a chicken and made chicken broth from the bones. I also kept a few pieces of meat to add to the broth to give it more flavor.
I know you can freeze the broth and use it for later but specifically how many times can I reuse the bones to make broth? Is there a time when it loses flavor or is not good for you? Does it differ depending on the animal/meat?
Beef bones can be used multiple times, but less flavor and gelatin will be extracted from each additional use. Harold McGee's "On Food and Cooking" describes this.
Because a standard kitchen extraction of eight hours releases only about 20% of the gelatin in beef bones, the bones may be extracted for a second time, for a total of up to 24 hours. The resulting liquid can then be used to start the next fresh extraction of meat and bones.
I would imagine chicken bones would be similar, although, since they are smaller, the first batch may be more effective than 20%.
You can use bones to make broth only once, all the goodness gets cooked out of them the first use. You could re-cook them for hours and get nothing from them.
The flavor of a good broth is gained by the liquid extracting the flavors and substances from the bones over a period of time. If your stock/broth has decent flavor, then, naturally, the bones should have little to none left to give any subsequent attempts at extraction.
Ideally, the answer should be "none" if you've made a great broth or stock on the first try.
