Fracture intermittency during a puncture test of cereal snacks and its relation to porous structure

The puncture test is widely used to assess the quality of cereal snacks. The number of fractures, which cause sudden force reductions observed in force–distance curves obtained during the puncture test, has been proposed to be a good predictor of sensory crispness. We used a stochastic model to determine fracture occurrence in two types of porous cereal snacks: Senbei (a Japanese rice cracker) and Ebisen (a flour-based snack). We studied the frequency distribution of the number of fractures for a single test. The observed variance to mean ratio of the numbers of fractures exceeded unity. On the basis of point process theory, this observation indicated a clustering of fractures. Correspondingly, the distance between successive fracture events was approximated more accurately by a power-law distribution than by an exponential distribution. Exponential distribution was a better distribution for intervals longer than 0.5 mm for Senbei, suggesting random or quasi-periodic occurrence of clusters.