Vol. XXIV · Bread Plate 9 of 12oven spring, baking bread, steam, crust, Maillard, Dutch oven, covered pot, internal temperature, done, 96 °C, scoring, ear, baking stone, 烤面包HM

Baking and Oven Spring.

A loaf baked in a covered pot for its first twenty minutes rises higher and shines. The lid traps the loaf's own steam.

A loaf goes into a hot oven at about 26 °C. For the next several minutes it grows quickly — oven spring — for the same reasons a soufflé rises (XVII.9): the gas in its cells expands as it warms, water and alcohol evaporate into the cells, and the yeast, warmed towards its optimum, makes a last burst of gas before it dies near 50 °C. The spring stops when the outer layer dries and sets into crust, and the crumb inside sets as its starch gelatinises and its proteins coagulate (VII.1). Anything that keeps the surface moist and extensible longer lets the loaf spring further.

That is the job of steam. Water vapour condensing on the cold dough keeps its surface wet and below 100 °C (II.3), delaying the crust by several minutes; it also gelatinises the surface starch into a thin film that browns glossy and crackles. Bakery ovens inject steam; at home a covered pot (Dutch oven) traps the loaf's own steam for the first 20 minutes, then the lid comes off so the crust can dry and brown (VIII.2). The loaf is done when its centre reaches about 96–99 °C for lean breads (88–93 °C for enriched ones, XXIV.10) and it sounds hollow when tapped. The workshop bakes with and without steam.

Below: the surface temperature of a baguette-sized loaf in a 230 °C oven, with steam or without (thermal bench: steam modelled as more water on the surface), the minutes before the crust dries and sets — the window for oven spring — and the browning after the time you choose.

What you will learn

Explain oven spring.
Use steam or a covered pot.
Get a crisp, brown crust.
Tell when bread is done.

Workshop

Thermal bench: a 60 mm cylinder of bread composition (USDA) from 26 °C in a 230 °C oven; steam represented as 0.5 kg/m² of surface water against the usual 0.12. The model heats the crumb more slowly than a real rising loaf, whose gas cells carry steam inward, so only surface timing and browning are shown. Done temperatures: common baking guidance.

Wet first, then dry and brown

In this model the dry-baked loaf's surface stops being wet and starts to set after about 2.6 minutes; with steam, after about 7.4, giving the loaf several more minutes to spring. At fifteen minutes the dry loaf has browned to 0.21 on the teaching index and the steamed one to only 0.05 — which is why steam is removed after the first 15–20 minutes, so the second half of the bake can dry and colour the crust.

Method for a crusty loaf at home: preheat the oven with a baking stone or a lidded cast-iron pot inside to 240–250 °C for 45 minutes; turn the proofed loaf onto paper, score it (XXIV.8), lower it into the pot and cover; bake 20 minutes; uncover, lower to 220–230 °C and bake 20–25 minutes more until deep brown; check the centre with a probe (96–99 °C) or tap the base for a hollow sound. Cool on a rack at least an hour: the crumb is still setting and steaming, and cutting it hot makes it gummy. Without a pot, pour a cup of boiling water into a tray at the bottom of the oven as the bread goes in.

At the stove

Bake two small loaves from one dough: one in a covered pot for the first 20 minutes, one on an open tray. Compare height, crust colour and shine.

The "ear" on a well-baked loaf — the raised flap along a score — forms when steam keeps the surface extensible and the cut was made at a shallow angle; bakers prize it as a sign of good fermentation, shaping and oven spring together.

Terms

Oven spring: The rapid rise of a loaf in its first minutes in the oven.
Steam: Water vapour that keeps the crust soft and moist early in the bake.
Dutch oven: A heavy lidded pot that traps a loaf's own steam.
Done temperature: About 96–99 °C inside for lean breads.

Oven spring lasts until the crust sets. Steam (or a covered pot) keeps the surface moist for longer, so the loaf springs higher and shines; then dry heat browns it. Lean bread is done at 96–99 °C; cool before cutting.

Sources

A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.
H. McGee, On Food and Cooking: The Science and Lore of the Kitchen, 2nd ed., Scribner, 2004.
USDA FoodData Central, SR Legacy (April 2018), public domain.