From Cooks Illustrated
[quote]What’s the best way to store bread?
We tested several storing several artisinal breads (Olive-Rosemary, baguettes) at room temperature, in the refrigerator, and in the freezer. When stored at room temperature, within just three days the loaves were shrunken, discolored, and firm—in other words, they staled. The same bread, stored in the refrigerator, fared even worse, hardening within a day or so. Why? According to food scientists, the major reason that bread stales is not moisture loss, but rather a process called retrogradation, in which the starch molecules in the bread crystallize. Retrogradation occurs about six times faster at refrigerator temperatures (36 - 40 degrees) than at room temperature, thereby making the refrigerator the worst choice for bread storage. However, the retrogradation process does slow down significantly when bread is stored below freezing temperatures. The water molecules in the bread freeze, which immobilizes the starch molecules and prevents them from forming crystalline structures.
Because retrogradation is accelerated by cold temperatures, it’s logical that it would be reversed by heat. Anyone who has ever softened stale bread in an oven or microwave has witnessed retrogradation reversal. Ovens don’t add moisture, but when stale bread (bread with crystallized starch) is heated to temperatures above 140 degrees, the crystals break down, softening the bread, (140 degrees is the gelation temperature of wheat starch—that is, the temperature at which the molecules form a gel).
To minimize retrogradation, store bread at room temperature—for up to two days—in a container that minimizes moisture loss (tightly wrapped in foil or in a zipper-lock bag). After two days, wrap bread tightly wrapped in foil, place in a freezer bag, and freeze. Thaw the slices at room temperature, or in the microwave or oven. (For a frozen full- or half-loaf, we recommend heating the bread, still wrapped in foil, in a 450-degree oven for 10 to 15 minutes, then crisping it by removing the foil and returning it to the oven for a minute or two.) If you find yourself with stale bread, wrap it in plastic wrap and reheat briefly in a microwave, but be prepared to use it almost immediately as retrogradation will set in again fairly quickly. Finally, only refrigerate bread that you’re intending to reheat (e.g., toast or grill) later on.[/quote]