Vol. IV · Knives, Tools and the Work Space Plate 5 of 10cut size, cooking time, carrot, boiling, slab, cube, thicknessHT

Cut Size and Cooking Time.

Cut a carrot into shreds, dice and chunks and boil them together: the shreds are tender while the chunks are still hard at heart.

Plate II.2 showed the square law on potatoes of different sizes; here it is on the cook's side of the board. One carrot is cut three ways — 2 mm shreds, 10 mm dice and 25 mm chunks — and all go into the same pot of boiling water. Each is done when its centre reaches about 85 °C, where its cell walls have softened (XX.2).

For pieces that are not cubes, the dimension that matters is the smallest one: a long thin shred heats from its two broad faces across 2 mm, however long it is. That is why slicing thinly is the fastest way to speed cooking without changing the heat, and why a recipe's timing breaks as soon as the cut changes.

Below: how far the centre of each cut has softened in boiling water, and the minutes each takes to become tender.

What you will learn

See the square law in the cook's own cuts.
Identify the controlling dimension of a piece.
Predict how a change of cut changes timing.
Use cut size to control doneness in a mixed dish.

Workshop

Carrot pieces from 20 °C into boiling water (thermal bench): a 2 mm shred treated as a slab, 10 mm and 25 mm cubes as spheres of the same width. The curves are the softening of the cell walls at the centre (a first-order reaction that runs fast only near 100 °C, course parameters); tender is taken as 60 % softened.

Heat in, then the walls give way

In boiling water a 2 mm carrot shred is tender in 4 min, a 10 mm dice in 4.8 min, and a 25 mm chunk in 9.3 min — 2.3 times as long. Two clocks run one after the other. First heat must reach the centre: the shred's centre is hot within 13 s, the chunk's only after 4.4 min, by the square law. Then the cell walls must soften, which takes a few minutes even at 100 °C whatever the size. For thin pieces the second clock dominates; for thick ones the first adds more and more.

Use this when one dish holds several ingredients. In a stir-fry, cut the slow ones (carrot, bamboo shoot) thinner than the quick ones (pepper, bean sprouts), or blanch them first (XVI.2). In a stew, cut the vegetables that should stay firm larger. And when a recipe says "simmer 20 minutes", it means for its cut; halve the size and the heating part of the time falls to about a quarter, while the softening part stays the same.

At the stove

Do the experiment: shreds, dice and chunks from one carrot, in one pot. Remove one piece of each every minute and bite it. Write down the minute each is tender; compare the ratios with the workshop's.

Professional kitchens often blanch the slow vegetables for a stir-fry or a sauté in advance and refresh them in iced water, so that at service everything only needs the same minute in the pan.

Terms

Controlling dimension: The smallest dimension of a piece, which sets how fast heat reaches its centre.
Tender: Cooked until the cell walls have softened enough to bite through easily.
Blanching: Briefly boiling and then chilling food, often to pre-cook slow ingredients (XVI.2).
Shape factor: How shape (slab, cylinder, sphere) changes heating at the same thickness.

Cooking time is set by the thinnest dimension, squared. Cut slow ingredients thinner, or start them earlier.

Sources

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.