Staling is often attributed to a loss of moisture from bread. But on a
microscopic scale, there’s a lot more going on.
The flour used to make bread contains high quantities of starch molecules.
In their natural state, these form a crystalline, highly organised structure.
Adding water to the flour undoes this structure, allowing the starch molecules to take on a more disorganised, gel-like arrangement
that gives bread a soft, fluffy texture when it comes out of the oven. As bread starts to cool, water leaves the starch and moves into other parts of the mixture, allowing starch molecules to return to their crystallised state.
It’s this recrystallisation – not drying – that makes bread go hard, and it happens even in humid conditions.
Keeping bread in the fridge doesn’t help.
In fact, recrystallisation happens faster at cooler temperatures. Freezing, however, dramatically slows the process, which is why bread can be successfully stored in a freezer.