Why does bread go stale faster in the fridge?

Because staling is not drying out — it is a chemical change in the starch, and that change happens fastest at fridge temperature.

When bread bakes, starch granules absorb water and swell into a soft, open structure. As the loaf cools and ages, those starch molecules gradually re-organise themselves back into tight, ordered crystals, squeezing out the water they were holding. The process is called retrogradation. The bread does not lose that water to the air — the water is still inside the loaf, just no longer bound up in a way that makes the crumb feel soft. This is why stale bread feels dry and firm even in a sealed bag.

Retrogradation runs fastest a few degrees above freezing, which is almost exactly the temperature inside a domestic fridge. Bread stored at around 4°C stales several times faster than the same loaf left on the counter. Below freezing the molecules cannot move enough to re-crystallise, so a freezer effectively stops staling altogether.

That gives a simple hierarchy. Bread you will finish within two or three days is best kept at room temperature in a bread bin or paper bag. Anything longer should be sliced and frozen, then toasted straight from frozen.

There is one honest exception. In a hot, humid kitchen, mould can spoil a loaf before staling becomes the limiting factor, and refrigeration does slow mould growth. If your bread is going green rather than hard, the fridge is the lesser evil.

Staling is also partly reversible. Heating bread above about 60°C melts those starch crystals again, which is why a stale roll warmed briefly in the oven tastes noticeably fresher — though it will re-stale faster once it cools.