## 1 Introduction
These conditions are essential for maintaining the authenticity of the bread's texture and pocket formation. While this study investigates thebaking process under one set of conditions and a specific dough formulation, it provides valuable insight into the fundamental aspects of the process. This rapid baking causes the dough to puff up, forming a pocket, and results in a distinctive soft texture with a slightly crispy crust [20]. The temperature profiles during baking are critical for understanding the heat transfer mechanisms and their impact on bread quality. Studies have shown that the temperature on the dough's surface rises rapidly, while the core temperature increases more slowly [21]. This temperature gradient is essential for the formation of the crust and the pocket [22; 23]. Mass loss during bread baking is primarily due to water evaporation [24; 25]. The rate of water loss affects the bread's texture and shelf life. Lebanese bread, due to its thin structure and high baking temperatures, experiences significant water loss compared to other bread types [26]. The final water content is a critical quality parameter, influencing the bread's softness and storability [27]. The expansion of the dough during baking is influenced by the production of carbon dioxide and the rapid vaporization of water [28; 29]. The high baking temperatures cause the water in the dough to quickly turn into steam, leading to pocket formation. The extent and uniformity of this expansion are key quality attributes of Lebanese bread [30]. While this mechanism is generally recognized in bread baking [31; 32], recent studies have shown that, in thin, double-layered Lebanese flatbreads (~1.5 mm), water vapor plays an even more dominant role due to the dough's low thickness and high permeability. The characteristic expansion and pocket formation in Lebanese flatbread is primarily driven by the buildup of internal steam pressure during baking. As water within the dough rapidly evaporates due to high heat, the resulting vapor increases pressure between the dough layers, forcing them apart and inflating them, resulting in a characteristic balloon shape [8; 10]. A recent study has also explored non-conventional baking methods, such as partial vacuum environments, to reduce baking temperature while still achieving proper pocket formation, confirming the critical role of water vapor phase change under varying pressure conditions [33]. Recent reviews emphasize the importance of integrating empirical and physics-based models to capture volume change and expansion in food processes like baking [34] and increasingly focus on optimizing both nutritional quality and traditional sensory attributes by understanding the physicochemical and rheological transformations during the baking process [5; 35]. This study uniquely investigates the high-temperature, rapid baking process of Lebanese flatbread, employing an instrumented oven to monitor both temperature and expansion in real time. The use of custom-built experimental equipment and empirical modeling of temperature--expansion relationships in this context is a novel approach, contributing new insights into heat transfer and mechanical behavior while baking. This study aims to investigate mass loss, expansion, and temperature evolution during the baking process of Lebanese bread. It aims to understand the relationship between temperature changes and bread expansion and provides empirical models to describe the temperature and expansion profiles during baking. The contribution is not only technical but also practical: the findings provide empirical foundations for modeling heat and mass transfer, understanding pocket formation mechanisms, and optimizing process conditions for quality control. This work addresses a significant gap in the literature by providing high-fidelity, real-world data on temperature, expansion, and water behavior in Lebanese flatbread baking.