why does starchy food like bread become hard and stale when it dries out
Staling One important mechanism is the migration of moisture from the starch granules into the interstitial spaces, degelatinizing the starch. The starch amylose and amylopectin molecules realign themselves causing recrystalisation. This results in stale bread's leathery, hard texture. Additionally, pleasant "fresh" flavor is lost to the air, and often unpleasant flavor is absorbed from it as well, especially in a confined space with other food such as when in a refrigerator.
History of bread The most common source of leavening in antiquity was to retain a piece of dough (with sugar and water in) from the previous day to utilize as a form of sourdough starter.[7] Pliny the Elder reported that the Gauls and Iberians used the foam skimmed from beer to produce "a lighter kind of bread than other peoples." Parts of the ancient world that drank wine instead of beer used a paste composed of grape must and flour that was allowed to begin fermenting, or wheat bran steeped in wine, as a source for yeast.