But as the bread cools, the starch molecules begin to return to their original tight granules, and in the process, expel the water that they absorbed during baking. As the starch granules contract, they get hard again and less flexible, making the bread dry and crumbly. Cooler temperatures cause the starch granules to contract faster, while warmer temperatures allow the granules to hold their water longer. In the freezer the process of becoming stale is almost stopped, but just above freezing, bread gets stale the fastest. So for the freshest loaf, either freeze your bread quickly or keep it at room temperature. Bread that goes stale in a plastic bag doesn’t really lose its moisture and can be improved by toasting. This is because the heat of the toaster causes the starch granules to reabsorb some of the moisture lost as the bread was becoming stale.