Why does stale food get hard?

Answer 1

Sometimes when I don't know the answer to a question, I ask the reverse and I ask variations of the same question. So... Why doesn't stale food get hard? When is it stale? What foods become stale faster than others? Why does de-staling bread by sticking it in the microwave (briefly) work? (Briefly!) What's the difference between stale and rancid? The underlying thread is moisture. A food is consider stale in part when it's taste changes. Taste is imparted more effectively with moist breads than dry. Staleness is a quality of foods whose moisture differs when left at room temperature for a while. The freshness of baked goods probably relies on residual CO2 and H2O production, from the yeast. Flat breads which don't rely on yeast for their taste and texture, don't go stale as fast. But in the end, they all dry out. Foods which do not rely on their moisture, such as nuts, do not typically go stale. If anything, foods like this become rancid with time (room temperature meat). This is a chemical decomposition, not a loss of water. About the de-staling of bread in the micro. 15 seconds moistens it up, probably because the baking process causes minor yeast activity, in turn leading to CO2 and H2O as by-products. Eat it fast however, because once that baby cools, you've got a rock on your hands.