So even though it was the middle of the night, I wondered what exactly is the process by which food goes stale? Also, does the process of going stale happen in the same way in different foods, but the result is different because the food itself is different? Or do different kinds of foods go stale in different ways?
Sliced bread might be fantastic and all, but because it's been sliced, it will go stale that much more quickly.
(Image from the Foreign Policy Association)
- Bread goes stale when the starches are exposed to air and crystallize.
- Specifically what happens is the water molecules present in the bread move. Normally, they're all mixed together with the starch molecules. But when the bread is exposed to air, the water molecules separate from the starch molecules. The starch molecules then form unbroken chains of protein, and that's what makes the bread tough.
The amylose molecules above are normally branching out in all directions, all over the place. But as they cool, they line up and form tight chains, forcing the water out from between them. This is basically what happens when bread gets stale.
(Portion of a diagram from University of British Columbia course page on Bread Staling)
- When you eat stale bread, not only will it seem tough, it may also seem dry. But in most cases, the water present in the bread hasn't actually evaporated; it's only left the starch chains and moved elsewhere in the bread.
- This process, by the way, is called starch retrogradation. I won't test you on that term or anything. I just thought you might like to know the phrase the food experts use for "that bread is going stale."
- Depending on the type of bread, it can go stale as quickly as a single day.
- The water molecules tend not to separate from the starches as quickly in breads that are lighter or less dense -- a baguette, let's say, as opposed to a pumpernickel. So perhaps that's why baguettes can hang around in the relatively open air at markets and in France without seeming to go stale.
The fact that lighter, airier breads don't go stale as quickly as other types of breads might be why baguettes can stand around naked in baskets like these without too many ill effects.
- Also, ingredients like egg whites and true buttermilk act as natural emulsifiers in bread. So if you're looking for bread that will stay fresher longer, look for egg or buttermilk in the ingredients.
- Emulsifiers, by the way, keep one liquid equally dispersed and co-existing in another. If you make vinegar & oil dressing, for example, you know that the vinegar and oil will separate unless you keep shaking it. An emulsifier would keep those two liquids co-mingling. Emulsifiers in starchy food will help keep the water mixed throughout the starches. Therefore, they help keep bread from going stale as quickly.
An emulsifier helps keep the starch molecules from lining up and forcing the water out, thus keeping the bread fresher longer.
(Image from Asia Pacific Food Industry)
- If your bread has gone stale, provided it isn't too far gone, you can reinvigorate it. If you heat the bread to a temperature above 140 F or 60 C, the bread will soften again.
- Specifically, what's happening here is that wheat starch is also influenced by temperature. If bread is at a temperature below 140 F or 60 C, that's when the crystallization process starts, and the starch chains begin to form. So if you warm the bread back up above that temperature, the water molecules move back into the wheat chains and everything softens up again.
- I've thought for a long time that if you keep bread in the refrigerator, it will last longer, which is true of most foods. However, since the starches crystallize at cooler temperatures (below 140 F or 60 C), the wheat chains will form even faster if the bread is in the refrigerator. In fact, refrigerated bread will go stale up to six times faster than room-temperature bread.
Though your refrigerator may call to you to feed it your bread, as this refrigerator seems to be doing, resist! Put your bread in the freezer, or else keep it out of the fridge entirely.
(Photo of Siemens refrigerator from UK Home Ideas)
- So, if you want your bread to stay fresher longer, keep it at room temperature. The downside to this plan, though, is that mold will grow faster on the bread at room temperature.
- If you keep your room-temperature bread in an airtight container, that will help slow the process of spoilage.
- However, even with your airtight container -- and everybody knows how hard a truly airtight container is to come by -- perhaps the best option is to freeze your bread right away.
- Freezing temperatures are too low for the starches to crystallize, so once the bread has cooled down past the refrigeration temperature and reached freezing, it won't go stale. The only trouble is, now you have frozen bread.
- But then of course you can always heat it up again, which, as we now know, will help those starch chains get remoisturized and relax.
- As far as other types of food going stale, Play-Doh, which is essentially dough and therefore contains starches, is susceptible to going stale. This is why the folks at Hasbro make their Play-Doh with an additional combination of ingredients that try to inhibit the process of starch retrogradation -- see, I did use that term again.
Play-Doh owes its wonderfully soft and pliable texture to all the extra ingredients that Hasbro's developers have added to keep this dough from going stale.
(Photo from Restoration Hardware. Hi, Mark & Jarred!)
- In general, it does seem to be true that bread or any starchy foods -- crackers, tortilla chips, cookies, etc. -- require that their water molecules and starch molecules to intermingle in order to stay "fresh." How quickly those foods go stale seems to depend on what type of starches are present in the food, how it was originally baked, and how much air it is exposed to and when.
- Actually, the whole process of going stale seems to depend mainly on the movement of water molecules. Nuts, for example, will get soft over time. In their case, water has not left the building, so to speak, but has been absorbed into the nuts, which is what makes them soft and chewy.
- Agricultural and food scientists are still studying the process by which food goes stale. As with so many things in the scientific world, this process is not yet entirely understood.
- P.S. Wine can go stale, too, when it's exposed to air for too long. Nobody seems to understand the details of this process, they only know that it does. But the fact that wine does go stale is why wine-maniacs -- er, aficionados say they will never order wine by the glass in a bar or restaurant.
While red wine does improve its flavor if allowed to breathe for a bit before you drink it, after a while any wine will go stale, lose its flavor, and eventually turn vinegary on you.
(Photo by dms246 on Flickr)
If you want lots more molecular-level detail about the process of starch retrogradation, check out Lab Cat's blog entry on Starch.
Oh, and just for kicks, here's this little bit of nostalgia about a loaf of bread...
Harold McKee, Patricia Dorfman, Justin Greene, On Food and Cooking, pages 541-542 (Google books)
Dr. Knowledge, "Does bread go stale faster when kept in the fridge or when stored at room temperature?" The Boston Globe, December 31, 2007
James BeMiller, "Why does food get stale over time?" Scientific American, April 24, 2008
Lab Cat, Water Activity
recipetips.com, glossary, Stale
Beppi Crosariol, "Wine by the glass? I'll pass," The Globe and Mail, July 30, 2008