Most people say bone broth should be cooked for a maximum of 72 hours. I've been going 6 days now. each day i drain out the liquid and refill the crock pot with fresh spring water. Although most if not all the collagen is gone, i have a hunch there's still lots of nutrients like calcium saturating the water each time the pot is filled. The broth has a fine light golden translucency each time, and tastes great. the bones are mostly sand at the base of the pot with a few pea sized bits. can i keep this going until all the materials have been consumed and nothings left in the pot? Waste nothing? I'm going to try this unless someone can give me a good reason not to :)
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You can cook the bones till they dissolve and eat it all in an ideal world and it wouldn't be a problem - the minerals and nutrients in the bones would be beneficial.
However, there is a problem due to pollution/ exposure of the animal to toxins (chemicals, heavy metals). Which is normal and would vary based on where the animals were reared and the quality of the environment there.
In the animals heavy metals such as lead accumulate in the bones and will be seeped into the broth increasingly the further you break down/ dissolve the bones.
The best is to cook the broth long enough to get the benefits from the gelatin from the bones, but not long enough so that the bones are dissolving themselves.
A couple of days on low heat is the roughly where you should keep your upper limit before the bones start dissolving more (this is a rough estimate of course, judge the broth yourself by checking visually for signs of bone decomposure).
To add to my previous non-answer, I've since tried reusing bones twice, and both times the second broth has gelled just fine. For beef broth I added one fresh additional bone the second time round, and for pork broth I didn't add any new bones, just the fresh water and vinegar.
I can't say anything about the nutritional content, but taste-wise they were just as good. There was definitely more sediment though so will need more straining. I didn't go for a third try, but I'll definitely re-use them at least once from now on!
Hmmm... I'd be interested in an answer to this, too. I cook my bone broth in the slow cooker for about 36 hours. The bones can be crumbly by that point but they're still fairly solid. Is it worth keeping those bones in for a second broth afterwards? Would I need to throw in some fresh bones too to get any benefit?
Sorry to answer your question with more questions!