Immediately after being removed from the oven, the loaf’s outer layer is very dry, around 15% water, and close to 400°F/ 200°C, while the interior is as moist as the original dough, around 40% water, and around 200°F/93°C. During cooling, these differences partly even themselves out. Moisture diffuses outward, and much of the loaf’s moisture loss occurs now. It ranges from 10% to 20% of the dough weight, depending on surface area, with small rolls losing the most and large loaves the least.
As the temperature declines, the starch granules become firmer and so the loaf as a whole becomes easier to slice without tearing. This desirable firming continues over the course of a day or so, and turns out to be the first step in the process called staling.