How does adding Lemon Juice or Vinegar help extract the Calcium from the Bones when making a Stock?

Bones are a combination of two kinds of substances: soft, organic cells and proteins, which are partly extracted into the water during the simmering of a stock, and a hard, inorganic mineral that doesn’t dissolve appreciably or contribute any flavor.

This mineral material in both bones and teeth is primarily a calcium phosphate compound called hydroxyapatite, which, as your dentist will hasten to inform you, is attacked by acids. (In the case of tooth decay, the acids are produced by bacteria.)

Unless the acid is very strong, it will take a long time to dissolve very much of the calcium phosphate in your soup bones. The small amounts of relatively weak acids in lemon juice, vinegar, or wine won’t extract much calcium, even after hours of simmering.

But if you want to have some fun, try this: Immerse a cooked and well-cleaned chicken bone (the thigh bone works well) in a covered jar of undiluted vinegar and let it soak for four or five weeks. The vinegar’s acid will dissolve enough of the hard hydroxyapatite so that mostly the soft, organic materials remain.

You will then be able to startle your friends by bending a very flexible chicken bone.

Tell them it came from a rubber chicken.