A large problem for fried snack products with a crispy crust and a soft moist interior is that the crust often loses its crispy character fast, in the order of 3¿20 min. As known during cooling of these snacks adherent oil will be sucked into the crust. The presence of oil in a cellular solid crispy material was found to affect the sound emitted on fracture dramatically, while it did not affect mechanical characteristics at least for shorter ageing times. Both the number of sound events and the acoustic energy released during fracture decreased. This could be explained by reflection of emitted sound at the oil¿air interface. Both the smaller number of acoustic events and the lower loudness will cause a decrease in crispy perception of the crust and in that way oil uptake during cooling of fried snacks can explain their fast decrease in crispness after frying.
van Vliet, T., Visser, J. E., & Luyten, J. M. J. G. (2007). On the mechanism by which oil uptake decreases crispy/crunchy behaviour of fried products. Food Research International, 40(9), 1122-1128. https://doi.org/10.1016/j.foodres.2007.06.007