What Makes Bread Go Stale?
An interesting little debate broke out in the comments to my post on women and processed food. One reader asserted that it's easy to bake bread at home for yourself: Just leave out the dairy, and store it in the refrigerator to prevent staling. Ladies, you can have inexpensive bread without excess salt and preservatives ... and also have your careers!
I'm sorry to report that this advice is pretty much exactly wrong. Many people think that bread goes stale because it loses moisture, producing that horrible, cottony texture that we've all come to know and regret in our homemade or bakery-fresh loaves. It turns out that this is not really correct. I quote Harold McGee's invaluablebook, "On Food and Cooking: The Science and Lore of the Kitchen":
Staling takes place in the days following baking, and seems to involve the loss of moisture: the bread interior gets dry, hard, and crumbly. It turns out that bread will stale even when there's no net loss of moisture from the loaf. This was shown in the landmark study of bread staling in 1852, when the Frenchman Jean-Baptiste Boussingault showed that bread could be hermetically sealed to prevent it from losing water, and yet still go stale. He further showed that staling is reversed by reheating the bread to 140° F/ 60° C: the temperature, we now know, at which starch gelates.
Staling is now understood to be a manifestation of starch retrogradation, the recrystallization, water migration out of the granules, and hardening that take place when cooked starch is then cooled (p. 548). The initial firming of the freshly baked bread loaf, which improves its ability to be sliced, is caused by the retrogradation of the simple straight-chain amylose molecules, and is essentially complete within a day of baking. The majority of starch molecules, the branched amylopectins within the granule, also retrograde. But thanks to their irregular structure, they form crystalline regions and expel water much more slowly, over the course of several days. This is the process responsible for the undesirable firming in texture after the bread has become sliceable.
To be clear: Bread left out also often becomes dry and hard, but this is in addition to the staling process, which will give your best fresh-baked bread the taste and consistency of a fresh-knitted blanket after a few days, even if you take care to keep it moist.
Sadly, you cannot retard the process by putting it in the refrigerator; in fact, McGee reports that "staling proceeds most rapidly at temperatures just above freezing, and very slowly below freezing." Refrigerated bread may stale up to six times faster in the refrigerator than it would if left on the counter in a paper bag.
There are a couple of things you can do to slow staling. The first is to add fat; fatty acids slow down the staling process, which is why pound cake keeps a lot longer than French bread. McGee recommends the emulsifiers found in "true buttermilk" (the kind left over after actually making butter) or egg yolks. The other thing you can do is to freeze the bread, which dramatically slows down the staling process. Bonus: Reheating bread will re-gelatinize the starches, giving your bread a soft, fresh texture.
The problem is that reheating bread also accelerates staling, meaning that once it cools down again, it will probably have a very unpleasant texture. So while this is an excellent strategy for dinner rolls, it is probably no good for making sandwiches to take to school or the office.
On the other hand, refrigerating bread is an excellent strategy for a store-bought, commercial loaf. Those breads are loaded with preservatives to prevent staling, and sticking them in the refrigerator combats the other two possible risks: drying out, and mold. I'm afraid that commercial bread really does win, on everything except taste.
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Megan McArdle at firstname.lastname@example.org