extensography

Extensography is a rheological test used in cereal science to characterize dough behavior under controlled extension. It is most commonly performed with an extensograph or extensometer, an instrument that stretches a dough sample while recording the force required and the resulting extension. The test provides information on gluten strength and dough elasticity and extensibility, which influence bread quality.

In a typical procedure, a dough piece of defined hydration and composition is prepared and allowed to relax. The dough is placed in a trough or on a frame and subjected to a biaxial extension by pulling at a constant rate. The instrument records a stress–strain curve from which parameters are derived, including the maximum resistance to extension (tenacity, often denoted R) and the maximum extensibility (Ed, in millimeters). The area under the curve corresponds to energy required for extension and, in some systems, additional indices such as the P/L ratio (the ratio of resistance to extensibility) are used to describe dough strength.

Applications: Extensography is used to evaluate flour quality for bread making, compare lines of flour or blends, guide formulation and fermentation conditions, and study how processing variables affect gluten network behavior. While informative, the method is highly dependent on test conditions such as hydration, temperature, and rest times, and results may not directly predict loaf volume.

History and standards: The extensograph device, notably the Brabender Extensograph, became widely used in flour milling and bakery research in the mid-20th century. Standardized procedures exist in various food-analysis organizations, though exact parameters vary by protocol.