Cooks Illustrated did a piece on bread storage --
Because many people store bread in the refrigerator, we were
intrigued by the number of products that claim to keep bread from
staling at room temperature. To compare the options, we purchased a
number of models: old-fashioned bread boxes made of wood and metal,
a stainless steel "canister" bread box (the lid is on the top), a
plastic-lined twill bag, expandable acrylic and plastic bread
keepers, heavy plastic bakery bags, and paper bags made from
polyethylene-lined "Freshness Paper". We measured moisture loss by
weight from both sandwich and artisinal bread stored at room
temperature in each model. We also stored one loaf of each type of
bread in the bag we purchased them in as well as one loaf of each
type in the refrigerator.
While a couple of the bread keepers did a good job at minimizing
moisture loss, within just three days all of the artisinal loaves
were shrunken, discolored, and firm - in other words, they staled.
The 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 F) 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.
Risa G noted that she can reverse the retrogation with the micro wave
and toaster.
CI noted
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 F, the crystals break down, softening the bread, (140 F is
the gelation temperature of wheat starch -- that is, the temperature
at which the molecules form a gel).
I leave it out a few days and then freeze after slicing. The slices
process through the toaster to make good morning toast for the rest of the week.