Modeling the transport phenomena and structural changes during deep fat frying

A fundamental model was developed to predict the heat and mass transfer that occur during the frying and cooling processes in deep fat frying of tortilla chips. Semi-empirical correlations were included to account for structural changes, such as shrinkage and expansion due to puffing. The finite element method was used to solve the sets of partial differential equations. The parameters that were studied included water saturation, oil saturation, temperature, and pressure.;The higher frying temperature resulted in a faster drying rate and a faster increase in the temperature and pressure of the product. More oil was absorbed at a lower frying temperature. In addition, due to the larger surface area, the thinner tortilla chip also absorbed more oil than the thicker chips during frying and cooling. Oil absorption appeared to seize once the temperature of the product begins to increase and a crust begins to form.;The formation of the crust layer led to excessive pressure buildup. Air and vapor trapped inside the pores began to expand as the temperature increased leading to puffing of the tortilla chip. The expansion of the tortilla chip began at about a water saturation of 0.20. The thickness of the tortilla chip was correlated to increase 100% near the center and progressively less moving away from the center. Shrinkage took place during the first few seconds of frying when the least bound “entrapped” water was removed. The radius of the tortilla chip was reduced by about 9.1%. Further frying led to removal of the more bound “vicinal” water. At equilibrium, only the most tightly bound “constitutional” water remained.;The cooling temperature had the most influence on oil absorption. The cooling temperature that was nearest to the temperature of the fried product led to the least amount of oil absorption. Oil absorption was assumed to be driven by capillary pressure difference and appeared to slow down as the temperature and pressure approached ambient conditions. The amount of oil absorbed was hypothesized to be directly related to the amount of oil that was saturated at the surface during the frying and the cooling processes.