Permeability of crust is key to crispness retention

Bread loses crispness rapidly after baking because water originating from the wet crumb accumulates in the dry crust. This water accumulation might be increased by the dense and low permeable character of the bread crust. Our objective was to investigate the influence of permeability of the crust on water uptake in the crust and on crispness retention. To achieve this objective, we increased the permeability of the control bread crust by creating small channels through the crust. The water vapour permeability of the crust with and without channels was measured using a newly developed method for brittle materials. Two further properties were measured over time: crispness of bread by analysing acoustic properties and water content of the crust. Control bread crust had low water vapour permeability and functioned as a barrier, leading to increased uptake of water in the crust. Water uptake was halved, however, if the water vapour permeability of the crust was doubled. As a consequence, crispness retention increased eight-fold; breads stored for four hours were as crispy as control breads stored for 30 min. We can conclude, therefore, that permeability of crust is key to crispness retention.