Vol. VI · Proteins and Heat Plate 6 of 11collagen, gelatin, braising, tough cuts, connective tissue, slow cooking, hoursMH

Collagen to Gelatin.

At 95 °C a shin of beef is tender in about three hours; at 70 °C it takes most of a day. Same reaction, different speed.

Working muscles — legs, shoulders, necks, the chest — are wrapped in a great deal of collagen, the rope-like protein of connective tissue. Briefly cooked, collagen first shrinks (VI.5) and the meat gets tougher. Held hot and wet for a long time, the collagen fibres slowly come apart and dissolve into gelatin, which turns the meat tender and the liquid around it rich and sticky.

This is a slow chemical reaction, and like all reactions it speeds up with temperature (V.10). A braise near the boil gets there in hours; a sous-vide bath at 70 °C takes a day or more, but keeps the muscle fibres juicier because they never get as hot (VI.5). The workshop shows how much collagen has dissolved over time at the temperature you choose.

Below: the fraction of collagen dissolved into gelatin against hours at four temperatures and at yours (course kinetics, activation energy 65 kJ/mol), and the hours to 90 %.

What you will learn
Workshop
First-order dissolving of collagen at constant temperature (course parameters: 0.010 per minute at 90 °C, activation energy 65 kJ/mol). Real cuts vary with the animal's age and the cut.

Hours, not minutes

At 95 °C, a gentle braise, 90 % of the collagen dissolves in about 2.9 hours in this model; at 80 °C in 7.1; at 70 °C in 13.5. Real cuts differ — older animals have more cross-linked, slower collagen — but the trade is general. Braises, stews, 红烧肉 and Sunday pot roasts work near the boil for a few hours; barbecue brisket climbs slowly through the 70s and 80s over a long day (III.5); sous-vide short ribs sit at 60–70 °C for one to three days and stay pink and juicy.

The gelatin is half the pleasure. It turns braising liquid glossy and lip-sticking, sets into jelly when cold, and coats the fibres in the mouth so that well-braised meat tastes moist even though its fibres have lost much of their water. Oxtail, pig's trotters, chicken feet and beef shin are prized in Chinese, French and many other kitchens for exactly this.

At the stove

Braise two pieces of beef shin in the same liquid, one at a bare simmer for three hours and one for one hour. Cool both in their liquid and taste. Then chill the liquid: the three-hour one sets firmer — more gelatin.

Gelatin was extracted commercially from bones and hides from the eighteenth century onwards; before that, cooks made jellies by long-boiling calves' feet, a laborious way of doing exactly this reaction.

Terms

Collagen
The tough, rope-like protein of connective tissue.
Gelatin
Dissolved, unravelled collagen; it thickens liquids and sets into jelly when cold.
Braising
Cooking slowly in a little liquid in a covered pot (XVI.4).
Cross-links
Bonds between collagen molecules that increase with an animal's age, slowing dissolving.
Collagen becomes gelatin slowly: hours near the boil, a day or more at 70 °C. Time and temperature trade.

Sources

  1. H. McGee, On Food and Cooking: The Science and Lore of the Kitchen, 2nd ed., Scribner, 2004.
  2. D. E. Baldwin, A Practical Guide to Sous Vide Cooking (2008–2012) and "Sous vide cooking: a review", Int. J. Gastron. Food Sci. 1, 2012.
  3. A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.