Viscoelasticity: Extensibility vs. Elasticity (Rheology)
Dough is a contradiction. It is a solid that flows like a liquid.
In physics, this property is called Viscoelasticity. It means the material has both viscous (flow) and elastic (snap-back) characteristics.
For the baker, understanding this balance is the difference between a loaf that spreads into a pancake and a loaf that springs into a high, airy dome.
The goal of fermentation is not just to create gas; it is to manipulate the rheology of the gluten network so it can hold that gas.
The Two Forces
Think of the gluten network as a net.
Elasticity (The Snap):
This is the dough's ability to return to its original shape after being stretched.
Source: Glutenin proteins.
Role: Structure. Without elasticity, the dough cannot hold its shape. It collapses [1].
Too Much: The dough fights you. It shrinks back when you shape it. The crumb is tight and dense because the bubbles cannot expand.
Extensibility (The Stretch):
This is the dough's ability to stretch without tearing.
Source: Gliadin proteins.
Role: Volume. Extensibility allows the gas bubbles to expand like balloons [2].
Too Much: The dough is slack and puddle-like. It flows outwards rather than upwards.
The Sourdough Factor: Acidity as a Relaxant
Commercial yeast dough is naturally very elastic (rubbery). It relies on additives (like L-cysteine) to relax it.
Sourdough has a built-in relaxant: Acid.
As the pH drops during fermentation, the acidity increases the solubility of the gluten proteins. This, combined with the enzymatic shearing from protease, softens the network.
Under-fermented dough: High pH. Tough, rubbery, hard to stretch [3].
Over-fermented dough: Low pH. Sticky, tearing, flows like soup (structure degraded) [4].
Achieving the Balance
The "Sweet Spot" for an open crumb is a dough that is highly extensible but still possesses enough elasticity to stand up.
You manipulate this balance through:
Hydration: More water = More extensibility (flow).
Salt: More salt = More elasticity (tightness) [5].
Folding: Coil folds build elasticity (strength) early in fermentation.
Time: Resting (autolyse and bulk) builds extensibility (relaxation).
Summary
Baking is not just chemistry; it is physics.
When you touch your dough, you are feeling for the balance between the "snap" and the "stretch." Mastering this tactile metric is the true craft of the sourdough master.
References
Dobraszczyk, B. J., & Morgenstern, M. P. (2003). Rheology and the breadmaking process. Journal of Cereal Science.
Wieser, H. (2007). Chemistry of gluten proteins. Food Microbiology.
Clarke, C. I., Schober, T. J., Dockery, P., & O'Sullivan, K. (2004). Wheat Sourdough Fermentation: Effects of Time and Acidification on Fundamental Rheological Properties. Cereal Chemistry.
Wehrle, K., et al. (1997). Effects of lactic acid, acetic acid, and table salt on fundamental rheological properties of wheat dough. Cereal Chemistry.
Beck, M., Jekle, M., & Becker, T. (2012). Impact of sodium chloride on wheat flour dough for yeast-leavened products. II. Baking quality parameters and their relationship. Journal of the Science of Food and Agriculture.
Belton, P. S. (1999). On the elasticity of wheat gluten. Journal of Cereal Science.
