A good stock is made by cooking the bones of meat or fish with vegetables and herbs in order to extract goodness, body and flavour. It forms the very foundation of cooking, in that even a quick vegetable stock will enhance the depth of flavour of your soup, stew, sauce or risotto. The better the stock, quite simply, the better your dish.
The key tenets of stock-making are simmering, skimming and reduction. Long, slow simmering breaks down the long protein chains in meat into amino acid building blocks such as glutamate, which creates a perception of savouriness that we call umami. But simmering also draws out particles of fat and blood that can coagulate and make your stock cloudy and dull. So the process is to simmer gently – in which the surface is disturbed by a few bubbles every few seconds – to extract the flavour and gelatin of the bones and meat, while constantly removing the impurities being extracted as well. Simple, right?
Skimming off any discoloured froth or scum is the key to a clear, sweet-smelling stock, especially in the first 15 to 20 minutes as you bring it up to a simmer. Use a large spoon or a flat, fine-meshed sieve to skim the surface (the words "hover like a hawk" spring to mind), then keep an eye on the stock throughout the entire process, skimming when necessary.
Timing is also key, with big, beefy, stocks taking up to four hours; sweet, fragrant chicken stocks, two to three hours; a simple vegetable stock, about 45 minutes; and a vegetable-based fish stock, 20 minutes. When done, strain the stock well, and consider the need for reduction. This means concentrating the flavour even more by bringing the stock to a boil, uncovered, allowing the liquid to evaporate and reduce by half. That is why we don't add much salt when making stock, as any reduction in liquid will increase the level of saltiness. Better to add salt to the final dish you make with the stock instead.
Stock made from fattier meats will require de-fatting. Skimming does this to a certain extent, and a sheet of paper towel can also be judiciously used, resting it flat on top of the stock to soak up the accumulated oils and fats. But the most effective way is to cool the stock and refrigerate it overnight, which will solidify the fat so that it can be easily scooped off. Use this technique for any meaty stews and soups.
When making stock, do whatever you can to add depth to its flavour, with lots of aromatics – onions, carrots, celery, any spices you like – and additional meats such as chicken wings to bolster the original bones. Always make a big batch of stock so you can cool and freeze it in various-sized containers, thereby giving you the perfect head-start on all future cooking.