The Kieffer dough and gluten extensibility rig - An experimental evaluation

Load-extension tests on flour dough are widely used by plant breeders, millers and bakers. The 'Kieffer dough and gluten extensibility rig' is a small-scale version of the Brabender extensograph, in which test pieces of about 0.4 g are extended. With the Kieffer rig, lower strain rates can be applied than in the Brabender extensograph and the experimental data can be expressed in terms of stress and strain. In this paper the performance of the Kieffer rig is illustrated by measurements on a weak and a strong dough. Formulas are given for the calculation of fundamental rheological parameters from the results of measure­ments with the Kieffer rig. Sagging and bending of the test pieces before measurements could be started, caused difficulties in the determination of the exact starting point of extension. The deformation was not purely uniaxial extension, because a shear component was also observed. The amount of dough that is extended did not increase throughout the test. This is probably due to the occurrence of a shear component fracture which occurred mainly near the hook. A relatively large variation in stress and strain at fracture was observed. The maximum in stress represents the strain at which the sample fractures macro­scopically better than the maximum in force. Variation in deformation history and volume of the test pieces have a negative effect on the reproducibility.