2001 AACC Annual Meeting Charlotte, North Carolina October 14-18, 2001 Charlotte Convention Center

The firmness of bread crumb is commonly measured by AACC method 74-09, which is an indentation technique. This test can also be used to derive firmness in fundamental units, such as can be obtained from a uniaxial compression test on excised crumb specimens. The objective of this study was to ascertain how well fundamental mechanical parameters of the bread crumb, such as compressive modulus and yield stress, could be predicted by the AACC method. Loaves were prepared from CWRS flour at optimal water absorption according to a short dough process, but to five different proof times. Cylindrical specimens were excised for compression testing, or whole slices used for indentation. Stiffness and critical load obtained from indentation were converted to elastic modulus and yield stress using standard formulae. Although relationships between the modulus obtained from compression and indentation gave reasonable fits (r(^2) = 0.84 and 0.87 for 100 and 5 mm/min, respectively), the values from indentation were higher for all proof times. It is surmised that high shear stresses at the indentor perimeter are responsible for the larger modulus. Larger values were also observed for the yield stress measured by indentation compared to its compressive counterpart (r(^2) = 0.90 and 0.94 for 100 and 5 mm/min, respectively). Larger values were ascribed to constraint of the stressed zone by its surroundings. If a universal calibration could be obtained for a wide variety of breadmaking conditions, it should be possible to predict fundamental values for the mechanical properties of bread crumb from AACC measurement of crumb firmness.