Stock is the foundation of professional cooking — literally 'fond de cuisine' in French. It's the slow extraction of flavour, gelatin, and minerals from bones, aromatics, and water. A properly made stock has body (from dissolved collagen), depth (from browned bones and mirepoix), and clarity (from patient skimming). It elevates every sauce, soup, braise, and risotto it touches. The difference between a home cook's soup and a restaurant's is almost always the quality of the stock underneath.
White stock: raw bones simmered gently with mirepoix. Brown stock: bones roasted at 220°C until deeply browned, then simmered. The roasting is where flavour develops (Maillard reaction). Chicken stock: 3-4 hours. Beef/veal stock: 6-8 hours. Fish stock (fumet): 25-30 minutes maximum — beyond that, fish bones release bitter compounds. Ratio: 2-3 parts water to 1 part bones by weight. Cold water start — extracting proteins gradually produces clearer stock. Never boil — gentle simmer only. Skim fat and impurities frequently.
For restaurant-quality stock: blanch bones first (bring to boil, drain, rinse) to remove blood and impurities. Then roast for brown stock, or proceed directly for white stock. A splash of vinegar in the water helps extract minerals from bones. Cool stock quickly (ice bath) and refrigerate — the fat solidifies on top and lifts off cleanly. Freeze in ice cube trays for convenient portions. The gelatin test: cold stock should jiggle like loose jelly — that body is what gives sauces their velvety texture without cream.
Boiling — turbulence emulsifies fat into the stock, making it cloudy and greasy. Not roasting bones for brown stock — you lose half the flavour. Adding too many vegetables — stock should taste primarily of the protein. Cooking fish stock too long. Not skimming. Starting with hot water — proteins coagulate on the surface and cloud the stock. Using too much salt — stock is a building block, not a finished product. Season at the sauce stage, not the stock stage.