The Science of Staling
When baked goods go stale, why does bread turn hard, while crackers soften?
According to our science editor, crackers are manufactured to be very dry to make them shelf-stable. Once the package is opened and the crackers are exposed to air, their sugars and starches start to absorb ambient moisture. After a few days, the once-crisp crackers will be soft and soggy.
When bread turns stale, an entirely different process takes place. Once exposed to air, bread starch undergoes a process called retrogradation: The starch molecules in the bread begin to crystallize and absorb moisture, turning the bread hard and crumbly.