Vol. I · What Cooking Does Plate 2 of 10temperature, time, oven, roast, gradient, doneness, grey bandHT

Two Dials: Temperature and Time.

The oven dial sets how hot the outside gets; the clock sets how far the heat travels inward. The difference between them is the difference between the edge and the centre.

A cook has two dials: how hot, and how long. Turn up the first and the outside of the food races ahead of the inside, because heat moves through food slowly. Turn it down and the whole piece warms more evenly, but it takes longer. The same centre temperature can be reached either way; what differs is everything between the centre and the surface.

The workshop roasts a 5 cm thick piece of beef from the fridge in two ovens and stops each when its centre reaches 54 °C, the usual target for medium-rare. Watch the centre and the surface, and compare how much of the meat has been taken past medium on the way.

Below: the centre and the surface of the roast in each oven, minute by minute, and the cut piece from each oven coloured by the highest temperature each layer reached.

What you will learn
Workshop
A 50 mm slab of beef from 5 °C, roasted in a still oven at the two temperatures you choose, stopped when its centre reaches 54 °C. Left: centre (solid) and surface (dashed) temperatures. Right: each piece cut open, coloured by the highest temperature each layer reached (red raw to grey well done).

Fast outside, slow inside

In the cool oven at 120 °C the centre takes 1 h 33 min to reach 54 °C and 10 mm of the 50 mm slab is taken past medium (above 62 °C); in the hot oven at 230 °C it takes 41 min, but 29 mm are past medium and the piece loses 25 % of its weight against 15 %. The hot oven is faster because the surface is hotter, and a hotter surface drives more heat inward each minute — but by the time that heat reaches the centre, the layers it passed through have been far hotter than the centre will ever be.

That is the whole tension of cooking anything thick: the surface wants heat (it is where browning happens, Vol. VIII) and the centre wants gentleness. Every technique in Part Four is a way of managing it — searing first or last (XV.7), resting (II.9), cooking in water at the target temperature (XVI.7). And it is why a thermometer, not the clock, says when meat is done (I.4).

At the stove

Next time you roast a piece of meat thicker than 4 cm, set the oven to 120–130 °C instead of 200 °C, put a probe thermometer in the centre, and take the meat out 3–5 °C before your target. Then sear it in a very hot pan for a minute per side. Compare the colour of the cut slice with your usual roast.

Whatever the oven, the centre must reach the safe temperature for the meat in question (Vol. XII); a low oven changes the path, not the destination.

The idea of cooking "low and slow" is old — braising and the bread oven cooling overnight are both ancient — but its use for tender meat cooked to a precise temperature owes a great deal to the twentieth-century work of Georges Pralus and Bruno Goussault on cooking in vacuum bags.

Terms

Temperature history
The temperature a food experiences over time; every cooking method is one.
Gradient
The difference in temperature from the surface to the centre.
Grey band
The layer of overcooked, grey meat between the crust and the pink centre.
Target temperature
The centre temperature a cook aims for, chosen for doneness and safety.
A hotter oven is faster but less even: the outer layers pass the centre's target long before the centre gets there.

Sources

  1. Y. Choi and M. R. Okos, "Effects of temperature and composition on the thermal properties of foods", in Food Engineering and Process Applications, vol. 1, Elsevier, 1986, pp. 93–101.
  2. A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.