## 3 Results and Discussion
### Expansion Measurements  
Expansion measurements show significant swelling in both the X (width) and Y (height) directions during the rapid heating phase, particularly as the core temperature approaches the boiling point of water (\(\sim\)100 \({}^{\circ}\)C). This supports the hypothesis that steam expansion and moisture loss are key contributors to pocket formation, even though internal pressure was not directly measured. This expansion is most pronounced in areas where steam accumulates beneath the dough's surface. Typically, the layers of dough have uniform thickness after baking [1; 3]. The expansion is documented through video recordings and regular snapshots during baking (Figure 7). As shown in Figure 7a, no expansion occurs in the first 4 s of baking. This phase is followed by the uniform formation of a few gas bubbles after 7 s, as shown in Figure 7b. At 8 s of the baking process time, a fast volume expansion occurs, and the bread gradually starts to inflate, taking an elliptical shape and reaching its maximum at the end of the baking period (Figure 7c,d). A pocket formation between two thin layers of baked bread is visible, resulting from the thermal expansion of gases during baking (Figure 3b). The expansions in the X (width) and Y (height) directions (Figure 4) measured during baking are presented in Figure 8. It shows the X (width) and Y (height) changes of the bread during the baking period for four representative tests conducted under identical conditions. These four tests were selected from a larger series of repeated trials based on their consistent dough preparation, baking profiles, and expansion behavior, providing a reliable basis for averaging and analysis. A slight continuous decrease in width (X direction) from 22 cm at the start to 17.5 cm at the end of baking is observed. A slight increase in the height (Y direction) at the beginning of the baking, reaching 25 mm after 7 s, is followed by a fast  
Figure 6: Surface color of baked Lebanese bread: (**a**) Upper surface (orange-brown), (**b**) Lower surface (light brown). Figure 7: Dough expansion at different baking times: (**a**) 4 s, (**b**) 7 s, (**c**) 10 s, (**d**) 12 s (end of baking). expansion, where the dough pieces' height increases from 25 mm to 100 mm in 4 s. A slight decrease in height is noticed at the end of the baking process. This is due to crack formation on the bottom surface of the baked bread and to gas leaking out, slightly reducing the pocket volume. On the other hand, small deviations in Y (height) expansion between tests are monitored. These variations may be attributed to minor differences in dough handling or proofing conditions, which could influence the initial dough structure and indirectly affect the location and behavior of pocket formation. However, it should be emphasized that, consistent with prior studies on flatbreads, water vapor expansion remains the dominant mechanism for pocket formation at high baking temperatures, while the contribution of CO2 generated during fermentation is considered negligible under these condition [51]. The test is repeated several times with identical initial conditions. The average uncertainty across these measurements is found to be approximately 1.8 mm and 2.2 mm on X (width) and Y (height) expansion, respectively. The maximum uncertainty is found around 5 mm and 6.5 mm on X (width) and Y expansion, respectively. These values are considered small for such applications. Figure 9 shows the average expansion in both directions along with the corresponding trendlines derived from polynomial regression analysis. Equations (4) and (5) also illustrate the average expansion in the X (width) and Y (height) directions concerning baking time, based on these empirical data.