Vol. XV · Dry Heat Plate 10 of 11gratin, oven dishes, lasagne, baked dishes, depth, browning the top, covering with foil, dauphinoise, baked rice, 焗HT

Gratins and Oven Dishes.

A potato gratin 5 cm deep at 200 °C has its top browned well before the middle is tender. Foil for the first part, then uncovered, puts the two on the same clock.

An oven dish has two clocks. The middle must heat through — potatoes softened, a lasagne hot at its centre — and that time grows with the square of the depth (II.2). The top must brown — the gratin crust, the bubbling cheese — and that time depends on oven temperature and how quickly the surface dries. In a shallow dish in a hot oven the two finish together; in a deep dish the top races ahead.

Cooks bring the clocks together with three tools: the depth of the dish (shallow cooks faster and gives more crust per portion), the oven temperature (lower for deep dishes), and covering — foil keeps steam in and the top pale and moist until the middle is nearly done, then comes off for the last 15–30 minutes to brown. A final few minutes under the grill (broiler) browns a top that is still pale. The workshop bakes a potato gratin.

Below: for the depth and oven temperature you choose, the minutes for the middle of a potato gratin to reach 90 °C and how brown the top is by then if baked uncovered (thermal bench), compared across depths and ovens.

What you will learn
Workshop
Thermal bench: potato in cream treated as potato, a slab of the depth chosen heated from top and bottom by an oven with wall radiation, from 20 °C until the middle reaches 90 °C (tender). Browning of the top on the course teaching scale; above about 0.8 the top is dark and likely over-browned.

Two clocks, one finish

At 200 °C a 30 mm gratin is tender in the middle in about 35 min in this model, its top still pale at 0.15 on the browning scale — a few minutes under the grill finishes it. A 50 mm gratin needs 73 min, and by then its top is at 0.87, over-browned: cover it with foil for the first half, or bake it at 170 °C, where the middle takes 87 min and the top browns more slowly.

Practical oven dishes. Choose a wide, shallow dish for more crust and even cooking; slice potatoes and vegetables thinly and evenly (a mandoline helps); start deep dishes covered and uncover for the last half hour; finish under the grill if the top is pale; rest 10–15 minutes before serving so the sauce sets and the inside evens out. Rice and noodle bakes (焗饭, baked macaroni) follow the same rules: hot filling, shallow layer, crust last.

At the stove

Make a gratin in two dishes, one shallow and one deep. Bake both uncovered at the same temperature and note which reaches tender first and which top is darker when it does.

Gratin comes from the French gratter, "to scrape": the crust that sticks to the dish and is scraped up was the prize. Hong Kong cafés (茶餐厅) made 焗饭 and baked pork chop rice a staple from the mid-twentieth century.

Terms

Gratin
A dish baked until a brown crust forms on top.
Covering
Foil or a lid that keeps steam in and stops browning.
Grill finish
A few minutes under the overhead element to brown the top.
焗
Cantonese for baking a dish in the oven, often with a cheese or sauce top.
An oven dish has two clocks: the middle (grows with depth squared) and the top. Shallow dish, hot oven; deep dish, foil first or a cooler oven.

Sources

  1. A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.