This is something I have been wondering about for a long time now…
Why is it that when soft foods get stale/old they get hard (e.g., bread, cheese, cake, etc.) but when hard foods get stale/old they get soft (e.g., carrots, crackers, chips)?
The food that makes me wonder about this the most are chocolate chip cookies. The ones that are hard and crispy when you buy them get soft, but the ones that are soft and chewy when you buy them turn hard!
Why don’t hard foods get harder and soft foods get softer?
BTW, if you have some stale hard chocolate chip (or other I suppose) cookies in a cookie jar, throw in a slice of fresh bread. Overnight, the bread becomes rock hard and the cookies become soft again.
A carrot has a lot of moisture, so by that argument it will give off moisture to the air and get dryer. That sounds about right, as an old carrot definitely LOOKS drier. But it gets soft, not hard, as it loses moisture.
I agree that there is some process by which moisture is moving into or out of the food in order to reach some kind of equilibrium with the surrounding environment. But that doesn’t really answer the question of why soft gets hard and hard gets soft.
Example: take a slice of bread and an initially hard chocolate chip cookie and put them on the kitchen counter. Come back a week later. The bread will be totally hard and dry. The cookie, soft and somewhat wet. They are both driving toward equilibrium with the same atmosphere, but they are both heading toward different moisture contents to reach that equilibrium. Why doesn’t the cookie lose all of it’s initial moisture and become as dry as the bread? Why doesn’t the bread get a little hard and the cookie a little soft and both end up with the same moisture content?
Bread starts with a fairly high water content and loses almost all of it. Crackers and crisp cookies start out dry, but the sugar or salt tend to absorb water. In air with the same humidity, their final water content will be different.
The carrot depends more on structure. Its cells start out puffed up to capacity with water, and collapse as the water evaporates.
Bob the Random Expert
“If we don’t have the answer, we’ll make one up.”