Stocks.
A good chicken stock sets to a wobbling jelly in the fridge. That jelly is collagen from the bones, turned to gelatin by hours of heat.
A stock extracts three things into water. Flavour: amino acids, peptides, nucleotides and aromatics from meat and vegetables (XI.5), most of it in the first hour or two. Gelatin: collagen from bones, skin and joints dissolves slowly, by the same reaction that tenderises a braise (VI.6), and needs hours. And, unwanted, fat and protein particles that cloud the liquid. A white stock (fond blanc) starts from raw bones; a brown stock from bones and vegetables roasted first for Maillard depth (VIII.1). Chicken bones give gelatin in two to four hours; beef and veal bones, older and more cross-linked, need six to eight; feet, wings and joints are richest.
Clarity is a matter of temperature. At a bare simmer, around 85–95 °C, proteins coagulate into a scum that rises and is skimmed, and fat floats in a layer; the stock stays clear. At a rolling boil, the turbulence breaks fat into tiny droplets and keeps protein particles suspended, and gelatin stabilises them: the stock turns cloudy — which Chinese cooks use on purpose for milky 奶汤 (XXII.2). Starting bones in cold water and bringing them slowly to a simmer gives the cleanest scum. The workshop extracts gelatin.
Below: the gelatin in a stock from the bones, amount, temperature and time you choose (course gelatin kinetics, slowed for cross-linked beef and pork bones, with a teaching share of each bone's collagen that can be extracted and evaporation from a lid ajar), against the level at which a stock sets when cold.
- Explain what a stock extracts.
- Choose bones and time for body.
- Keep a stock clear.
- Make white and brown stocks.
Hours for body, a simmer for clarity
In this model a chicken stock with 0.6 kg of carcasses per litre has about 1.0 % gelatin after two hours and 1.6 % after four — enough to set; chicken feet and wings give about 3.3 % in three hours. Beef knuckles, whose collagen is more cross-linked, have converted only about 0.57 of it in four hours against 0.91 for chicken, giving 1.3 % gelatin, and reach 3.1 % only after eight — which is why veal and beef stocks simmer all day. More bones per litre give more body directly; more time gives diminishing returns once the collagen is mostly converted, while the vegetables' fresh flavours fade.
Method for chicken stock: put 1.5 kg of carcasses, wings and feet in a pot with 2.5 litres of cold water; bring slowly to a bare simmer and skim the grey scum as it rises; add onion, carrot, celery and a few peppercorns after the first skimming; keep at a bare simmer, lid ajar, for 3–4 hours, never boiling; strain without pressing, cool quickly in shallow containers (XII.7), refrigerate, and lift off the fat when cold. For brown stock, roast the bones and vegetables at 220 °C until well browned first, deglaze the roasting tin (VIII.7) and add tomato paste. Salt stocks only at the end of whatever they become (XXII.8).
Make stock from chicken carcasses, refrigerate a cup overnight, and tip the cup: does it hold as a jelly? Note how many hours you simmered.
Terms
- Stock (fond)
- Water flavoured and given body by long simmering of bones and aromatics.
- Gelatin
- Dissolved collagen; gives body and sets when cold (X.8).
- Skimming
- Removing the coagulated protein scum that rises.
- Mirepoix
- Onion, carrot and celery for flavouring stocks and sauces.
Sources
- A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.
- H. McGee, On Food and Cooking: The Science and Lore of the Kitchen, 2nd ed., Scribner, 2004.