Stock is water that has extracted flavour and gelatine from bones and vegetables. Doing it well requires understanding what is being extracted and what conditions damage it.

Gelatine

The collagen in connective tissue converts to gelatine with prolonged moist heat.

Which is what gives stock body — the quality that makes a sauce coat a spoon rather than running off.

Joints, feet, wings and knuckles are richest in collagen, which is why they are used despite having little meat.

A stock that sets when chilled has extracted gelatine successfully, and that is the practical test.

Temperature

The critical variable and the most commonly wrong.

Stock should never boil. A gentle simmer, with occasional bubbles breaking the surface, is the target.

Boiling agitates the liquid, emulsifying fat and suspending fine particles, which produces cloudy stock that cannot be clarified afterwards.

Which is why clear stock and cloudy stock differ almost entirely in how they were heated rather than in ingredients.

Skimming

Proteins coagulate and rise as scum during the early stage.

Removing it produces a cleaner result, and it is worth attending to for the first twenty minutes and unnecessary afterwards.

Starting with cold water helps, since proteins are drawn out gradually and coagulate at the surface rather than being sealed in.

White and brown

White stock uses raw bones, producing a delicate result suited to light dishes.

Brown stock uses roasted bones, producing colour and the deep flavour from Maillard reactions, suited to robust preparations.

Which is a genuine difference in application rather than a quality hierarchy.

Vegetables

Added later than bones, since they release their flavour faster and break down with prolonged cooking.

Which is why adding them at the start produces a muddy vegetal note.

Onion, carrot and celery are conventional, and the proportions are less important than avoiding anything that dominates.

Brassicas turn sulphurous with long cooking and are generally avoided. Starchy vegetables cloud the stock.

Salt

Stock should be unsalted or barely salted, since it will be reduced and used as a component.

Which is the most common mistake in commercial stock, where salting for immediate palatability makes it unusable for reduction.

Time

Chicken stock is generally complete within a few hours. Beef and veal take considerably longer, since the collagen is more resistant.

Fish stock takes under an hour, since prolonged cooking extracts bitterness from the bones.

Vegetable stock takes least of all and deteriorates with extended cooking.

Which means a single cooking time applied to everything produces one good result and several poor ones.

Storage

Cool quickly, which for a large quantity means dividing into shallow containers rather than refrigerating a hot pot.

Fat rises and sets, forming a seal that extends refrigerated life, and it can be removed before use.

Freezing in portions is the practical approach, and reducing stock substantially before freezing saves space, with water added back on use.

Whether it is worth it

Honestly, for a household that cooks a lot, yes, and it happens mostly unattended.

For a household that cooks occasionally, good commercial stock exists and the difference is smaller than enthusiasts claim.

The middle path is saving bones and vegetable trimmings in the freezer until there is enough to justify a pot, which costs nothing and produces something genuinely better.

Pressure cooking

Substantially faster, since higher temperature accelerates collagen conversion.

Which produces good stock in a fraction of the time, with a slightly different character since the sealed environment retains volatile compounds that would otherwise escape.

The result is cloudier, since the liquid moves more, and for most uses that does not matter.

Bone broth

A marketing term for stock cooked longer, and the health claims attached to it are considerably weaker than the promotion suggests.

Collagen consumed is digested into amino acids like any protein rather than being deposited where it is wanted.

Which does not make it bad — it is nutritious and pleasant — and the specific claims are unsupported.

Vegetable stock

Different in kind rather than a substitute, since there is no gelatine and therefore no body.

Which means it flavours without thickening, and dishes relying on stock for texture need another approach.

Roasting the vegetables first adds depth that raw ones cannot provide.

Using the trimmings

Onion skins, carrot ends, celery leaves, herb stalks and mushroom stems all contribute and are otherwise discarded.

Collecting them in a freezer bag until there is enough costs nothing and produces something from waste.

Clarifying

A raft of egg white and mince, simmered gently, traps particles and produces a genuinely clear consommé.

Which is a classical technique requiring care, and it is unnecessary if the stock was simmered gently in the first place.

Straining through fine cloth handles most of what matters for ordinary use.

Commercial alternatives

Quality varies enormously, and the better products are refrigerated or frozen rather than shelf-stable cubes.

Checking the salt content matters most, since heavily salted products cannot be reduced.