To prepare a stock, the ingredients should be selected and used appropriately. This includes the removing of grit and the chopping up of bones (so as to extract the best flavours from meat), and the selecting of the contents and combinations of the “mirepoix” (a diced vegetable mix that is gently cooked over a long period). Seasoning must also be considered and usually includes the addition of pepper (but not salt) and herbs such as thyme or rosemary.
Stocks are cooked by submerging all ingredients in a pot of cold water. As the water heats up, impurities (like fat and coagulated blood) can be collected from the surface of the liquid. As soon as the liquid reaches a boiling point, it should be brought down to a simmer and then left to cook for several hours (in the case of beef and chicken stock) or just 20 minutes (for a fish stock). Throughout the cooking process, a skimming spoon should be used to remove any excess fat that rises to the surface. Once done, a soup ladle can be used to separate the stock liquid from the bones, vegetables and herbs.
To store, stocks should be cooled down to room temperature before being placed in a metal or plastic container that can fit easily into the refrigerator or freezer. The cooling process will push more fats and oils to the surface of the stock, but in this instance these should be left to help seal the stock and prevent air from getting to it and spoiling it. If refrigerated, below 5°C, a stock will last around 5 days (after which the flavour will start deteriorating). Frozen stocks can keep for over 2 months.
When needed, the stock can be reheated (for at least 10 minutes), the surface fats removed and the remaining liquid added to the soup, stew or sauce for which it is intended.