Continuous boiling will impart a cloudy appearance to the final product and although the taste will not be affected it won't be as appetizing looking in my opinion. I like to roast the bones first to get a nice flavour and to help give a lovely colour to the final product. There are no hard and fast rules for proportions of ingredients but as I have a pot which holds approximately 5 Imperial gallons I like to use somewhere in the neighbourhood of 20lbs worth of bones and then fill the pot with cold water till the bones are covered.
Usually I add a couple of peeled carrots, a couple of cooking onions, the green parts of leeks if I have them on hand, a bunch of parsley, several garlic cloves (I love garlic and usually use a whole head), a tablespoon of whole peppercorns and if I'm making beef broth a couple of bay leaves and about a 2 inch finger of peeled ginger.
But no salt. Ever. Salt is something that is used in the final product and I'd never add salt at this stage because I like to control the amount of salt and sometimes I reduce the liquid to create a demi-glace.
Once the liquid has heated to just below the boiling stage (small bubbles just beginning to break the surface) the heat is immediately turned down to the lowest possible temperature, covered and left to simmer ever so gently for at least 12 hours. Now that may sound like an extraordinary amount of time but I leave my stockpot on my stove overnight. In the morning I pour the liquid through a fine mesh sieve into a clean pot and then leave the liquid to cool until I can place the pot into the fridge.
Here's where the cold nights come in because if it is refrigerator cold outside I love to place the pot outside on a balcony or deck until it is cool enough to go into the fridge. As the liquid cools the fat hardens and is then easily skimmed off to leave you will a totally fat free delicious treat.
As unglamorous as it looks...
...this shows the fat that will be left after the beef broth was cooled. There was at least a 2" slab of beef fat but fortunately it was easy to skim off. The liquid has turned to a jelly as it is so stock full of rich marrow and succulent flavour. The finished product...
...full of marrow bone goodness!
Now all that is left is to package it up in containers and stock it in the freezer waiting patiently for use.
Next up...Steak and Kidney Pie using the beef stock to make a rich gravy.