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Why does bread go stale?

The short answer

Bread firms up as it cools and sits because some of its starch gradually rearranges after baking. Water also moves within the loaf and can escape into the air. Staling is not simply a matter of all the bread’s water drying out.

What baking does to starch

Wheat flour contains a lot of starch. During baking, heat and water make the starch absorb water and swell, changing its original structure. This change is called gelatinization. It helps give the inside of fresh bread its soft, moist texture.

Starch slowly rearranges as bread sits

After bread cools, some starch molecules gradually form more ordered arrangements. Amylopectin, one of the components of starch, plays a major role in this change. The rearrangement is called starch retrogradation. It is one of the main processes involved in bread staling: the crumb becomes firmer even if the loaf does not lose all its moisture.

Water moves, too

Water can move between the soft inside of the bread, called the crumb, and the outer crust. As some water moves toward the crust or escapes into the air, the crumb can feel drier and the crust can soften. These changes in moisture distribution happen alongside starch retrogradation, and together they affect the bread’s texture.

A bag can slow water from escaping into the air, but it does not stop the starch from changing. That is why bread can become firmer even while it is wrapped and does not look dry.

1. Some starch rearranges

Starch in bread gradually rearranges Soon after baking, starch molecules are shown in varied shapes. As the bread sits, some form more ordered arrangements. The drawing simplifies what happens to the molecules. Freshly baked As it sits

Some starch molecules slowly form more ordered arrangements.

2. Water can move from crumb to crust

Water moves within a loaf Some water in the soft crumb moves toward the outer crust. This does not mean all the water leaves the bread. Crust Crumb

Moisture shifts between the inside and the crust.

Both changes affect the crumb’s texture. The bread does not need to lose all its water to become firmer. The molecules and moisture movement are simplified here.

Will a refrigerator keep bread soft?

Not always. In one study of white bread, starch crystallized faster at refrigerator temperatures than at room temperature. The result can vary with the type of bread and how it is stored, so the same finding may not apply to every loaf.

Bread’s texture changes through more than visible drying. Starch rearrangement and the movement of water both matter. Together with the way bread rises, these changes show how much a food’s texture can depend on what happens to its ingredients during and after baking.

References