The Science behind Bread Staling

Are you familiar with the term bread staling? Well it refers to these undesirable changes (other than microbial spoilage) that take place between the time bread is baked and consumed. Bakers that understand the different aspects of staling and the factors that affect them can take better decisions about their formulas, ingredients, processes, and packaging.

The Science Behind Bread Staling

Crumb firming is caused by changes in starch structure. The starch in wheat flour is made up of straight and branched chains contained in granules. During baking the starch granules swell and the straight chains diffuse out. Then, as the bread cools, the straight starch chains link together to provide the loaf’s initial shape and strength. The starch branched chains will remain in the granules during baking and slowly link together during storage, making the crumb increasingly firm with time. Moisture changes also contribute to staling as evaporation and water redistribution take place. Evaporation can cause a 10% weight loss in unwrapped bread but remains below 1% in wrapped bread. Even without a change in moisture level, wrapped bread will taste dry because of water migrating from the crumb to the crust and from the starch to the gluten. The crust softening in wrapped bread is also caused by that water migration, as its moisture level goes from about 12 to 28 %. This changes the dry, crisp, pleasant texture of fresh crust into the soft, leathery, unpleasant texture of stale crust. Flavor losses and changes will also occur: the taste of fresh bread is usually a combination of sweet, salty, and slightly sour, but with age the sweet and the salty diminish and the remaining sourness starts to become unpleasant. The aroma of fresh bread is usually yeasty and wheaty, but with age the pleasant volatile alcohol smell of yeast is lost, the wheaty aroma is reduced, and the remaining doughy or starchy aromas become unpleasant.

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