extensographs

An extensograph is a laboratory instrument used to measure the rheological properties of dough, especially its resistance to extension and its extensibility, under a standardized stretching protocol. It is a common tool in flour quality testing and bread research, helping assess gluten strength and dough behavior during mixing and fermentation.

In a typical test, a dough sample prepared from flour and water is conditioned and formed into a standardized piece, which is clamped between two jaws. The machine then elongates the dough at a controlled rate while a force transducer records the resisting force, producing a curve of resistance versus extension or time. From this curve, two primary parameters are read: Extensibility (Ex), the maximum length the dough can extend before rupture (measured in millimeters), and the resistance to extension (R, or Ri), the peak resistance encountered during extension. The shape of the curve and the area under it give indices of gluten strength, elasticity, and dough development.

Interpretation and use: Extensograph results support flour grading and blending decisions, formulation of bread-making processes, and quality control of flour lots. They help distinguish flours suited to bread versus pastry or cookies, monitor changes during storage, and detect additives or processing effects that alter dough rheology.

Variations and history: Extensograph-type devices have been produced by several manufacturers, such as Brabender and Chopin, and the test substrate and reporting conventions have evolved over time. The term is sometimes used interchangeably with extensogram, though procedural details may differ.