WHY COARSE TOASTED RUSK ROLLS ARE CRISPIER THAN FINE ONES

Toasted rusk rolls with a coarser structure are sensed crispier than those with a fine structure, at the same water activity (aw). The present paper shows that this difference in crispness perception is related to differences in fracture behavior and accompanying acoustic emission. Both sensory and instrumentally determined crispness decreased gradually with increasing aw in roughly the same manner for both coarse and fine products. Nevertheless, the coarse rusk roll was perceived as being crispier than the fine one. Typically, in the coarse structure the measured “Number of Force Drops” of a relatively large size and the “Number of Sound Events per cross section area” of relatively large intensity were more numerous than in the fine one. Our data show that relatively large force drops and sound events are related to the more intense crispness perception and stronger sound sensation for the coarse structure toasted rusk roll. We propose the “Total Sound Energy per cross section area” and the “Mean Sound Event Intensity” to be primarily responsible for the higher crispness perception of the coarse rusk over the whole aw range.