Extractives are the flavouring components in meat and browned vegetables that dissolve in the cooking liquid — the soluble substances that make a stock taste of meat. They include free amino acids, small peptides, nucleotides like inosinate, and the Maillard products of browning: the compounds that give beef tea its savour, that distinguish a long-simmered stock from hot water. Lean meat is rich in them, fat carries little — which is why a stock’s flavour lives in the lean and the bones’ marrow rather than the dripping. The cook’s art with extractives is solubility management: starting in cold water to draw them out, simmering gently to keep the liquid clear, reducing to concentrate them. They are flavour in solution — the reason stock is the foundation of savoury cooking.