It is a common scenario: You eat two slices of artisan sourdough toast for breakfast and feel energised. That night, you eat two slices of pizza and feel like you have swallowed a bowling ball. The ‘bread’ ingredients are identical: Flour, water, salt, yeast.

The only reliable clock is the dough itself. To read it, you must stop looking and start touching. These are the three Tactile Metrics that every sourdough baker must master to judge the invisible biology of the jar.

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.