When we think of food going stale, we typically think of products such as bread. You might think that bread starts to stale days after it is made. But the process of staling actually begins as soon as the loaf leaves the oven and begins to cool. How quickly bread goes stale depends on what ingredients are in it, how it was baked, and the storage conditions.

Breads are essentially networks of wheat flour protein (gluten) molecules and starch molecules. Suspended inside this scaffolding are pockets of carbon dioxide gas that are produced during fermentation by yeast. This creates a foamlike texture.

The most important event in the process of staling is when starch molecules crystallize. The starch molecules need water molecules to form their crystal structure.  They get the water molecules from the gluten. As a result, the network changes, becoming rigid at room temperature and below. This state, however, is reversed with the introduction of heat; stale bread can be freshened by warming it—as in toasting.

Although scientists have made considerable progress in dissecting the staling process, it remains poorly understood. Yet progress has been made in slowing staling through the addition of certain ingredients so that bread from large commercial bakeries in the U.S. seldom goes stale. On the other hand, the process of staling has also been sped up by other methods in order to make croutons in a relatively short time.

7 Comments

1. 1. JBrooksy 11:28 PM 4/25/08

   I'd be nice to know what those "certain ingredients are and their relationship to our health,

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2. 2. Victoria Burmester 01:29 AM 4/26/08

   Interesting, but not nearly enough detail. Links to further reading would be useful, too.
   V Burmester, London

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3. 3. starsandy 07:10 PM 4/27/08

   Yes, there is interesting analysis but only on the surface level. Bread is the main thing we think about when food goes stale but what about rancid oil, what is happening there. What is the relationship between going "stale" and spoilage due to microbes?

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4. 4. gvgoebel 06:43 PM 4/28/08

   What I have always wondered is why do hard foods get soft when they get stale and why do soft foods get hard when they get stale? No doubt a conservation law of some sort at work.
   
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   Edited by gvgoebel at 04/28/2008 12:07 PM
   
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   Edited by gvgoebel at 04/28/2008 6:38 PM

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5. 5. tanjie 01:54 AM 4/29/08

   Rancid means unpleasant odor due to spoilage of fatty foods. This is simply a breakdown of the fatty chains in reaction with molecules in the air, mainly moisture. Some can look at this as a method of self-decomposition. Others call it auto-oxidation. In either case, over time, carbon chains from the fatty acid backbone become unstable and break off. As cooking can change the taste and smell of foods, so does self-decomposition. Except that there is nobody cooking this stuff - it's self 'cooking'. It's a sort of reaction out of control, spiraling away. This is an example of chaos theory, where ordered atoms become disordered on their own, spontaneously.

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6. 6. berniev 11:19 PM 4/30/08

   I have noticed that the bread sold under the retail grociers' brand in my area always goes stale in 2 to 3 days at room temperature.
   It developes an organic order as well. Whereas the commercial bakery brand can go a week or more without going stale. I would like to know what causes that organic odor.

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7. 7. jwcnmr 08:47 AM 1/13/10

   There is a much longer explanation in Harold McGee's book"On Food and Cooking."

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