ICSE Class 9 Answered

Wheat flour, the primary ingredient of bread dough, is made of starch. Starch, in its natural state, is largely in crystalline form. Once mixed with water to form a dough and baked in the oven at high temperatures, the crystalline structure of the starch breaks down as the starch absorbs water and becomes increasingly amorphous.

As the bread cools, however, the starch begins to slowly regroup into a more ordered, crystalline structure again, and gradually returns to the crystal state that causes bread to harden and grow stale. Likewise, when the moist bread is kept in the refrigerator, the moisture begins to disappear casuing the bread to harden and turn stale. 

Bread which is not moist can ke kept in the refrigerator for a day or so. It still remains fresh and consumable.