Permeability measurement and gas retention in double-layered flatbread

During the baking of double-layered flatbreads, delamination occurs when the internal flow of water vapor within the flatbread's porous structure significantly exceeds its escape to the outside. This makes the gas permeability of the dough a critical factor in pressure build-up. Data on bread crust and the layers in double-layered flatbreads are scarce but essential for a better understanding of the baking process. This study investigated the gas permeability of double-layered flatbreads baked at 300 °C for varying durations, with and without steam injection, using a specially designed two-chamber experimental apparatus. The study revealed low permeability values in both the upper and lower flatbread layers (ranging from 6 × 10^-17 to 3 × 10^-15 m²). During delamination, the detachment of the upper layer leads to a more rapid increase in its permeability. The experimental work was complemented by numerical simulations to assess the relevance of permeability to gas generation in the dough. The simulations confirmed the primary role of water vapor compared to carbon dioxide in pressure build-up. The permeability must be below 8 × 10^-13 m², regardless of oven temperature (100, 200, 300, 400 °C), to allow for a relative pressure increase in excess of 10 kPa. The greater the permeability, the longer the time taken for pressure to build up, all the more so when the temperature was low.