Mechanisms Determining Crispness and Its Retention in Foods with a Dry Crust - Food Colloids: Self-Assembly and Material Science - page 499

Other macroscopic properties affecting crust fracture behaviour are the
presence of sides supporting the crust and the curvature of the crust. The
presence of stiffer sides will support wedge penetration above three-point
bending of the crust during biting as long as the distance between the sides is
of the order of 10 cm or less, depending upon the mechanical properties and
thickness of the crust and the mechanical properties of the layer below. A crust
with convex curvature to the outside will also bend less easily than a flat crust.
Maybe this is a main reason why breads characterized by a crispy crust often
have a rounded shape - at least in one direction.
34.6 Conclusions
The crispy behaviour of dry cellular solids is determined by various mecha-
nisms acting at molecular, mesoscopic and macroscopic length-scales. On the
mesocopic scale it is especially the morphology at length-scales of 50-500 mm
that is of greatest importance for the crispness of the product. The minimum
and maximum sizes of the structural elements on the mesoscopic scale have
here been estimated from sound emission properties and mechanical and
physiological constraints. For a product consisting of a crispy crust and a
non-crispy moist inner part, the variation in mechanical properties over
macroscopic distances (41 mm) can also be important.
Acknowledgements
We thank EefJan Timmerman for performing experiments on the effect of oil
uptake by rusk rolls. The study was funded by the Wageningen Centre for Food
Sciences, an alliance of major Dutch food industries, Wageningen University
and Research Centre, Maastricht University, and TNO Nutrition and Food
Research, with financial support from the Dutch government.
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