Origin

Staling was once thought to be only caused by moisture loss from baked products. This theory was quickly disproved over 150 years ago. Now, it is associated with the retrogradation or recrystallization of starch molecules. It can even occur without water loss from the crumb.

How staling works

Staling occurs in products that contain starch, such as bread, buns and cakes. It begins immediately after bread comes out of the oven. Then, gelatinized starch starts to cool down to an ambient temperature and solidify, leading to retrogradation and molecular realignment.

Retrogradation of amylopectin in bread is a slow process. It is believed to be the major contributor to staling during storage. On the other hand, amylose retrogrades very quickly, during bread cooling. This is an advantage in slicing loaves without the product collapsing.1,2

Approaches to reduce staling in bakery products

Consumers often squeeze a loaf of bread before buying it to check its freshness. In this situation, they are assessing the elastic deformation of the loaf. A soft yet springy texture tells the consumer the bread is fresh. If the bread is too firm, the loaf is rejected as stale.

Strategies for delaying staling in bread are:1,2,3

Formulation Process
  • Emulsifiers as crumb softeners: do not produce softer fresh bread, but they do slow the rate of firming over time.
  • Amylases: maltogenic amylases of intermediate thermostability from fungal or modified bacterial sources can break down starch into dextrins and sugars. The latter can penetrate the starch helix structure and inhibit the realignment process.
  • Lipases: clean label emulsifier replacements which break down lipids to produce mono- and diglycerides that function as crumb softeners.
  • Hydrocolloids (gums): they bind and hold water, preventing moisture migration and reducing the firming rate.
  • High-sugar recipes: such formulations raise starch glass transition temperature, suppressing amylopectin recrystallization.
  • Long fermentations: using dough systems which require long bulk fermentation prior to dough mixing. For example, sourdough or yeast preferments like sponges.
  • Freezing: stops all chemical reactions and molecular motion, preventing starch from crystalizing after baking.
  • Process optimization: cooling variables such as time, temperature and RH can minimize excessive water loss  and slow down the rate of bread staling.
  • Product size optimization: Larger and thicker products stale at a slower rate than flat and small products.

Techniques used in assessing staling:4

  • Rheological methods: Uniaxial compression and pasting properties
  • Thermal analysis: differential scanning calorimetry (DSC)
  • Infrared spectroscopy: Fourier transform infrared (FTIR), near infrared (NIR) reflectance, and nuclear magnetic resonance (NMR) spectroscopy
  • X-ray diffractometry
  • Microscopy: Transmitted and polarized light, confocal laser scanning and electron
  • Sensory/organoleptic tests

References

  1. Cauvain, S.P. “Bread Spoilage and Staling.” Technology of Breadmaking, 3rd Edition, Springer International Publishing Switzerland, 2015, pp. 287–299.
  2. Rayas-Duarte, P., and Mulvaney, S. “Bread Staling.” Breadmaking: Improving Quality, 2nd Edition, Woodhead Publishing Limited, 2012, pp. 580–594.
  3. Cauvain, S.P. Baking Problems Solved, 2nd Edition, Woodhead Publishing, Elsevier Ltd., 2017, pp. 113–117.
  4. Kulp, Karel, J. G. Ponte, and Bert L. D’appolonia. “Staling of White Pan Bread: Fundamental Causes.” CRC Critical Reviews in Food Science and Nutrition 15.1 (1981): 1–48.