Dem bones are an essential ingredient in making a soup, stock, or stew, every bit as essential as the meat, vegetables, and seasonings.
Their purpose may not be obvious, however, if we think of them as hard, nonreactive mineral matter. Yes, their structural material is mineral: calcium phosphates, to be specific. But calcium phosphates don’t dissolve or decompose in hot water, so if that were all they were made of, we might as well add stones as bones.
They wouldn’t contribute any flavor to a stock.
But bones also contain organic, as opposed to mineral, materials, most notably cartilage (gristle) and collagen. In young animals, the bones can actually contain more cartilage than mineral matter, and cartilage contains collagen, a protein that breaks down into soft gelatin when cooked. So bones actually contribute a rich and unctuous mouth feel to the stock.
Shin and thigh bones, together with their connecting knuckle joints, are particularly rich in collagen. If you really want a stock or stew that will jell almost like Jell-O when cooled, add a collagen-rich calf’s foot or a couple of pigs’ feet. Cooked pigs’ feet cooled in their jelly is an old-fashioned country treat. If you make it, tell your guests it’s a fancy French dish called Pied de Cochon.
The hard parts of bones appear to be solid, but they contain a surprising amount of water, nerve fibers, blood vessels, and other stuff that would make an instant vegetarian out of you if I told you.
In Bones 101 you would learn that a typical bone is made up of three layers. The inner core is a spongy material containing lots of yummy organic matter and, in the hollows of the long bones, the even yummier marrow. That’s why, and this is important, we cut or crack open the bones before putting them in the stockpot. Outside the core is the hard, largely mineral layer followed by a tough, fibrous outer membrane called the periosteum.
But the bones we throw into the stockpot have hangers-on, too. Outside of a Halloween skeleton or an anatomy lab, have you ever seen a perfectly clean bone, without any meat, fat, gristle, or other connective tissue clinging to it?
Not likely. All those bits contribute greatly to the stock’s flavor. Moreover, they brown beautifully when we roast our veal bones before committing them to the pot when making a brown stock.
So save all your bones in the freezer for stock-making day. Or take advantage of the last thing in the world besides advice that is free or nearly free: bones from your butcher.