Effect of Geometric Eccentricity on Heat Transfer, Puffing Behaviour and Quality Attributes of Chapati

Unlike manual rolling, mechanical systems are more susceptible to systematic geometric errors arising from roller misalignment, feed mechanisms, and process parameters. Therefore, understanding the effect of controlled variations in eccentricity on chapati quality is essential for optimizing machine design and defining acceptable limits of geometric deviation in automated production. This study aimed to investigate the effect of geometric eccentricity on thermal distribution, puffing behavior, moisture dynamics, structural uniformity, and overall quality of chapati, and to establish its importance as a key parameter in rolling and baking processes. The study was conducted as an experimental investigation in the Food Engineering/Processing Laboratory, Jawaharlal Nehru Krishi Vishwavidyalaya. Chapati samples were prepared using whole wheat flour dough with a moisture content of 40–42%, and varying levels of eccentricity (e = 0.00–0.50) were introduced through controlled rolling techniques using manual and semi-mechanical methods. Eccentricity was calculated based on the geometric relation of an ellipse. Physical parameters such as major and minor axes, thickness distribution, and uniformity were measured using a digital vernier caliper. Puffing behaviour was evaluated through puffing height and puffing index, while moisture content was determined using the standard oven drying method at 105°C. Thermal characteristics, including surface temperature and temperature differences, were recorded during baking. Quality indices such as puffing uniformity, steam retention, moisture uniformity, browning index, and internal structure were also assessed, along with sensory evaluation by a semi-trained panel. The results indicated that increasing eccentricity significantly affected all quality parameters. Thickness variation increased from ±0.05 mm to ±0.55 mm, while puffing extent decreased from 98% to 10%. Puffing uniformity index declined from 0.95 to 0.15, and steam retention index from 0.96 to 0.12. Moisture loss rate increased from 1.20 to 1.55 g/min, and temperature difference rose from 2°C to 35°C. Moisture uniformity and browning indices also decreased substantially. It was concluded that eccentricity plays a critical role in determining chapati quality, and maintaining low eccentricity is essential for achieving uniform cooking, optimal puffing, and improved overall acceptability.