Why Does Bread Go Stale?
By the BrainSnail editorial team. How these articles are written and checked, and how to tell us when one is wrong.
Most people assume stale bread has simply dried out, and that is only part of the story. The main process is a change in the starch itself, which is why bread sealed in a bag still goes stale and why warming a stale slice briefly brings it back.
Staling is not drying out
Staling is mainly caused by starch retrogradation. During baking, starch granules absorb water and swell in a process called gelatinisation, which gives fresh bread its soft texture.
As the loaf cools and sits, those starch molecules gradually reorganise into a more ordered crystalline structure, squeezing out the water they held. The bread becomes firm and crumbly even though the water is still inside the loaf, just relocated rather than lost.
Where the moisture goes
Water released by the starch migrates outwards from the crumb towards the crust. This is why stale bread has the opposite texture profile of fresh bread: the inside becomes dry and firm while a once crisp crust turns leathery.
Actual evaporation does happen too, particularly in cut loaves and in dry air, which is why a cut face should be kept covered. But sealed bread still stales, which proves evaporation is not the main mechanism.
Why the fridge is a mistake
Starch retrogradation happens fastest at temperatures just above freezing, roughly in the normal fridge range. Bread kept in the fridge goes stale several times faster than bread left at room temperature.
The freezer is different and works very well. Below about minus eighteen degrees the process essentially stops, so freezing a loaf preserves it in near fresh condition. Slice before freezing and you can take out what you need.
How to bring stale bread back
Because staling is a reversible reorganisation rather than a loss, heat can undo much of it. Warming stale bread above about sixty degrees Celsius reverses a good deal of the crystallisation.
Practical methods:
- •Sprinkle with a little water and warm in a hot oven for a few minutes
- •Toast slices, which also drives off surface moisture for crispness
- •Steam briefly for soft rolls
- •Note that the effect is temporary and the bread will stale again faster afterwards
How to store bread properly
At room temperature in a paper bag or a bread bin is best for a crusty loaf, since paper allows some moisture exchange and keeps the crust from going soft. Plastic keeps the crumb softer for longer but ruins a crisp crust and encourages mould.
Choose according to how long you need. Eating within a day or two, leave it out. Longer than that, freeze it. The fridge is the one option that combines the worst of both, and stale bread is far from useless anyway, since it is the correct ingredient for croutons, breadcrumbs, bread pudding and several excellent soups.
Why some breads keep better
Not all bread stales at the same rate, and the differences come down to ingredients that interfere with starch recrystallisation or hold water more tightly.
Fat is the main one, which is why enriched breads like brioche and challah stay soft for longer than a lean loaf. Sugar attracts and holds moisture, so sweetened breads keep well. Sourdough resists staling because its acidity slows the process. Commercial bread often contains enzymes and emulsifiers that do the same job deliberately, which is a large part of why supermarket loaves stay soft for a week.
The takeaway
Bread goes stale mainly because starch molecules recrystallise and push out water rather than because the loaf dries out, the fridge accelerates this while the freezer stops it, and gentle heating temporarily reverses it.