Bread kept in a fridge firms up faster than bread left on a counter, which seems to contradict everything else about refrigeration. Staling is not spoilage, and it does not follow the same rules.
Staling is a change in the starch
Baking gelatinises starch, disrupting its ordered structure so it absorbs water and forms the soft texture of fresh crumb.
That state is unstable. The starch molecules gradually rearrange back towards an ordered form, expelling the water they held and stiffening the crumb.
The bread has not lost the water to the air. It has moved inside the loaf, which is why stale bread can be firm and damp at the same time.
Refrigerator temperatures are the worst case
Recrystallisation runs fastest at temperatures a little above freezing, which is precisely the range a fridge maintains.
A loaf chilled for a day can be as firm as one left out for several, and the effect is most obvious in lean breads with little fat or sugar.
Freezing avoids the problem entirely, because below freezing the molecules cannot rearrange, and a frozen loaf resumes staling only once thawed.
Warming reverses part of it
Heating stale bread above a certain point returns much of the starch to its disordered state, restoring softness temporarily.
This is why toasting or briefly warming a loaf makes it palatable again, and why the improvement fades within hours as the process resumes.
Each cycle recovers slightly less, since moisture genuinely evaporates during heating even though evaporation was not the original cause.
Ingredients slow the process
Fats, sugars, eggs and milk all interfere with starch reordering, which is why enriched breads stay soft for longer than a plain loaf.
Commercial bakeries add enzymes and emulsifiers that act on the same mechanism, extending softness across a longer shelf life.
This is the main reason a supermarket loaf and a bakery loaf age so differently, rather than any difference in freshness at the point of sale.
Storage should target the crust
A sealed bag keeps moisture in, which slows drying but softens a crisp crust into something leathery.
A paper bag does the reverse, preserving the crust while the crumb dries faster, so the right choice depends on which part matters.
For anything beyond a day or two, slicing and freezing preserves both better than any counter storage, because it stops the underlying chemistry rather than managing its symptoms, and slices can be toasted straight from frozen.