Vol. XXIV · Bread Plate 11 of 12staling, stale bread, retrogradation, bread storage, fridge, freezer, bread bin, reheating bread, toasting, crust, softness, amylopectin, 面包老化MS

Staling and Storage.

Put one loaf in the fridge and another in a bread bin. Two days later the cold one is staler, though it has lost less water.

A freshly baked loaf's starch is gelatinised: its chains are disordered and hold water (VII.1). As it cools and sits, the chains — first amylose, within hours, then amylopectin, over days — slowly line up into crystals and squeeze water out of the crumb into the crust: retrogradation (VII.3). The crumb firms and turns crumbly, the crust goes leathery as it takes up that water. Drying adds to it, but staling happens even in a sealed bag; it is a change of structure, not mainly of water.

Retrogradation is fastest a little above freezing, so bread in the fridge stales several times faster than on the counter, and frozen bread hardly stales at all. Warming stale bread above about 60 °C melts the crystals again: a loaf refreshed in a hot oven for a few minutes, or toast, is briefly soft and fresh — until it cools and restales faster. Fat, sugar, eggs and a 汤种 (XXIV.10) interfere with the crystals and keep bread soft longer, which is why enriched breads keep better than lean baguettes. The workshop stores a loaf.

Below: the firming of bread crumb over the days you choose stored on the counter, in the fridge or in the freezer (course retrogradation model, VII.3), for a lean loaf or one made with 汤种 and fat (a teaching factor), and how it compares at the end.

What you will learn
Workshop
Course retrogradation model (VII.3) at 21 °C (counter), 4 °C (fridge) and −18 °C (freezer), against hours. Enriched or 汤种 bread: firming × 0.7 (teaching factor shaped on published comparisons).

Counter for days, freezer for longer, never the fridge

In the course model a lean loaf has firmed to about 0.65 after a day on the counter and 0.89 after two, but to 0.98 after one day in the fridge and 1.00 after two; in the freezer, 0.03. So: keep bread you will eat in a day or two at room temperature in a paper bag, bread bin or cut-side-down on a board (crusty bread in plastic goes soft and leathery); slice and freeze the rest, well wrapped, the day it is baked, and toast slices straight from frozen or thaw them at room temperature.

Refreshing: sprinkle a stale loaf with water and put it in a 180–200 °C oven for 5–10 minutes; it softens inside and crisps outside — eat it the same day. Very stale bread becomes something else: toast, croutons, breadcrumbs, bread pudding, French toast, panzanella, ribollita, or the Middle Eastern fattoush (XXIII.7). Enriched and 汤种 breads, and those with more water, stay soft longer; sourdough's acidity also slows staling and mould (XXIV.7).

At the stove

Put two slices from one loaf in sealed bags, one in the fridge and one on the counter. After two days, press and taste both.

The French chemist Jean-Baptiste Boussingault showed in 1852 that stale bread had lost almost no water and that heating it restored freshness — the first evidence that staling is a change in the starch, not simply drying.

Terms

Staling
Firming of bread as its starch recrystallises.
Retrogradation
Gelatinised starch re-forming crystals as it cools (VII.3).
Refreshing
Reheating bread above about 60 °C to melt the crystals.
Freezer storage
The way to stop staling for weeks.
Staling is starch recrystallising, not drying. It is fastest in the fridge and stopped in the freezer. Keep bread on the counter for a day or two, freeze the rest, and reheat above 60 °C to refresh.

Sources

  1. A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.
  2. H. McGee, On Food and Cooking: The Science and Lore of the Kitchen, 2nd ed., Scribner, 2004.