Vol. VI · Proteins and Heat Plate 5 of 11doneness, myosin, collagen shrinkage, actin, juice loss, rare, medium, well doneMHF

Meat by the Degree.

Rare, medium and well done are not moods. They are temperatures at which particular proteins have set, and particular amounts of juice have gone.

As meat warms through the fifties, its myosin sets: the flesh turns from translucent to opaque and firms from soft to springy — rare to medium-rare. Around 60–65 °C the collagen sheaths around the fibres shrink, squeezing the fibres like a wrung cloth; juice runs and the meat turns pink-grey — medium. Above about 70 °C actin sets too, and the fibres turn dry, tight and stringy — well done.

Juice loss follows the same steps. Published cooking-loss curves for beef rise slowly to about 50 °C, steeply through the sixties as the collagen shrinks, and level off above 75 °C. The workshop shows, for the temperature you choose, which proteins have set, how much weight the meat has lost and the colour you would see.

Below: the share of myosin, collagen and actin set after ten minutes at your temperature, the meat's cooking loss (a teaching curve with the shape of published beef data) and its colour.

What you will learn

Link doneness names to temperatures.
Name what each protein does to texture.
Explain why juice loss jumps in the sixties.
Choose a target for a cut and a method.

Workshop

Set fractions after ten minutes at each temperature (course kinetics, midpoints from calorimetry). Cooking loss: teaching curve following the shape of published loss data for beef. The swatch is the course's doneness colour scale.

Three proteins, three textures

At 55 °C the meat is firm and opaque but collagen and actin are scarcely touched, and it has lost about 9 % of its weight. By 65 °C the collagen has shrunk and the loss is about 19 %; by 70 °C about 24 %, and by 75 °C, with actin set, 28 %. A steak cooked to 55 °C instead of 70 °C keeps roughly a fifth more of its weight — most of it juice.

That is why tender cuts — fillet, sirloin, rib-eye — are best cooked to the fifties: they have little collagen to soften, so heat beyond myosin only costs juice. Tough cuts with lots of collagen — shin, shoulder, brisket — must go far past this range and stay there for hours, until the collagen dissolves into gelatin (VI.6) and the meat falls apart, juicy again in a different way. Safety sets the floor for some meats regardless (XII.6, XVIII.2).

At the stove

Cook three thin slices of the same steak in a pan to 50, 60 and 70 °C at the centre, checking with a probe. Weigh each slice before and after, and taste them in order. Note the weight lost and the change in texture.

Doneness words differ by language: Chinese menus use 一分熟, 三分熟, 五分熟, 七分熟 and 全熟, roughly rare, medium-rare, medium, medium-well and well done; the temperatures behind them are the same proteins.

Terms

Doneness: How far meat has been cooked, judged by its centre temperature.
Myosin: The muscle protein that sets in the fifties, firming meat.
Collagen shrinkage: Contraction of connective-tissue sheaths near 60–65 °C, squeezing juice out.
Cooking loss: Weight lost in cooking, mostly water.

Myosin sets in the fifties (firm, juicy), collagen shrinks in the sixties (juice runs), actin sets above 70 °C (dry).

Sources

Differential scanning calorimetry of muscle: myosin denatures around 54–58 °C, collagen shrinks around 60–67 °C, actin around 70–80 °C (A. Wright, I. B. Leach and P. Wilding, "Differential scanning calorimetric studies of muscle and its constituent proteins", J. Sci. Food Agric. 28, 1977; H. McGee, On Food and Cooking, 2004). The course uses midpoints within these ranges.
A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.