efficient heat transfer between the bottom side of the food and the oil. The stage two (surface boiling) is characterised by the sudden loss of free moisture at the surface, increased surface heat transfer, and inception of crust formation. Crust formation occurred primarily at the bottom surface of the food, and it become thicker showing increased resistance to evaporation. As temperature increased, the crust formation decreases due to a higher rate of evaporation. The evaporation rate was higher before crust formation as was as tur- bulence within the oil. The convective heat transfer coefficient at the bottom surface decreased after the crust formation (Sahin et al., 1999a, 1999b). The oil turbulence caused by the bubbles leads to increase heat transfer rates. Some studies showed that when the water loss rate is very high the bubbles near the potato surface might hinder the heat transfer (Costa et al., 1999).