Analysis of the heat transfer coefficient during potato frying

The objective of this work was to study the dependence of the heat transfer coefficient (h) on the water loss rate of potato during frying. An indirect method was used where a metal piece with the same geometry of the potato pieces was placed on top of various potato samples at different frying times, and its temperature was recorded for 20-30 s. Another method consisted of direct recording of the temperature within a potato slice, close to the surface. Water loss rate was estimated by image analysis of bubbles. After immersion in hot oil, the potato temperature increases and water starts vapourising, leaving the surface in the form of bubbles that flow through the oil. The water loss rate increases until complete drying of the potato surface and then decreases till the end of. frying. The h value showed the same behaviour increasing up by two times in relation to the values measured in the absence of bubbling, with maximum values depending on the oil temperature and potato geometry (443-750 W m(-1) K-1). The percentage of heat transferred to the potato that is used for water evaporation showed an increase with time up to complete surface drying. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.