Cracks in bread crust cause longer crispness retention

Crispness is among the most important factors that the consumer uses to assess the quality of crispy bread. However, this quality attribute is rapidly lost after baking. It is known that crispness retention can be increased more than eight times by enhancing the water vapor permeability of the crust. Current methods to achieve this, i.e., puncturing the bread before baking, require an extra process step. We hypothesize that cracks that appear spontaneously on the crust surface after baking can also enhance water vapor permeability and therefore improve crispness retention. We were able to confirm this hypothesis by preparing composite breads containing the same crumb but different crusts, with crust recipes of varying starch/protein ratios. Crusts systems that were generally high in gelatinized starch content and poor in evenly distributed gluten were more prone to crack after the whole process of part-baking, freezing, and baking off. These cracks led to an increased water vapor permeability of the crust and an eight times longer instrumental crispness retention compared to standard bread. In this paper we also discuss possible causes for crack formation in the crust. We hypothesize that effective cracks are caused by thermal shock in materials with a low ability to dissipate energy.