Effect of potato orientation on evaporation front propagation and crust thickness evolution during deep-fat frying

The various theoretical approaches that have been proposed for modeling heat and mass transport during deep-fat frying of potatoes do not take into account the effect of potato orientation with respect to gravity. This can be partly attributed to lack of systematic experimental information at different orientations. The objective of the present work is to experimentally study the effect of potato orientation on the evaporation front propagation and crust thickness evolution and how this effect varies with frying conditions. To achieve this goal, a special device has been constructed which, among others, permits: (a) exposure of only one surface of a potato stick to hot oil, (b) rotation of this potato surface at 0°, 90°, and 180° with respect to gravity, and (c) accurate placement of miniature thermocouples under-but very close to-the exposed potato surface. Crust thickness is determined by 2 independent methods: (a) microphotography and (b) a micrometer. It is found that the evaporation front propagation and crust thickness evolution are different among the examined surface orientations. The fastest heat penetration and thickest crust are measured at vertical (90°) surfaces. The implications of this finding regarding potato texture and energy consumption are discussed.

Understanding the role of surface orientation on the crust evolution and the propagation of the evaporation front inside the food is of particular value to: • Deterministic modeling efforts of the coupled heat and mass transfer phenomena during deep-fat frying, and • food industry; the present data suggest that crispier food is produced and less energy is consumed when the food is placed at a nonhorizontal position inside the fryer.