Friend of The Food Geek, Craig, asks via Twitter,

Hi, Craig,

The writing staff ofThe Big Bang Theorykeeps on hand a staple of scientists from many fields in order to make jokes about all manner of nerdy topics fromString Theory physicstoSuper Mario Brothers. On this occasion, even though it’s not as lofty as a reference toThe Flash, they did know what they were talking about. Bread goes stale much faster in the refrigerator than it does sitting out on a counter.

Long-time readers may recall when we discussedwhether to wait until your freshly-baked bread should cool before you slice it or notthat the bread is coated in a thin layer of gelatinized wheat starch. When slicing freshly baked bread, this still-damp starch will stick together and ruin the structure of an otherwise lovely loaf. When left too long under the right conditions, the starch will crystallize. Crystallization means that its structure will become rigid and lose its pliability. When the starch becomes rigid, we say that the bread becomes stale.

For our purposes, there are two main methods by which the starch will crystalize. The most obvious way is if it dries out. If you’ve had a loaf of bread for a week* then you’ll notice your bread isn’t as soft as it used to be. This is mostly because the moisture escaped from the bread and the starch has dried some and crystallized.

If you store the bread in the refrigerator, then you cause the starch to crystallize quickly. This does not happen from dehydration but from the cold itself. It’s ironic, because normally we think of refrigeration as a way of preserving food. Like bananas, bread has a temperature that it prefers to be at, and lowering that temperature will cause problems. In this case, it causes the starch to gelatinize quickly. Whereas a store-bought loaf of sliced bread might last a week without staling on the counter, it can stale as quickly as one day in the refrigerator.

Not all is lost, however! Depending on the moisture content of the rest of your bread, you can still save it. The trick is that you have to heat the bread to 140°F in order to change the starch from a gelatinous state to a more pliable state, and you have to ensure that the bread is still moist. If your bread has really dried, then there’s not much you can do, but if it’s just cold, then the moisture combined with the heat will revive the bread. Of course, as I’ve mentioned, this only works if the bread hasn’t lost a lot of moisture, so you need to make sure that there’s no place for the water to go; wrap the bread well or nothing can save you from staleness.

The easiest way to reheat your bread is in a microwave. Just heat it for a 5 to 30 seconds, depending on your microwave, until it feels warm to the touch. You might even want to cover the slices of bread with a damp paper towel to help with the moisture. Remember, if you cook it too long, you’ll dry it out, but just enough to be nice and warm to the touch will probably do the trick. But you’ll save yourself the trouble for a lot longer by just not refrigerating the bread.

*-If you bake your bread or get it from a baker who does not pump it full of preservatives, then this process will happen within a day or so.