Modeling of oil dripping during deep-frying: New highlights to reduce oil uptake in fried products drastically

Abstract

Deep-frying is usually considered a single-step process involving immersion in a high boiling point liquid, commonly vegetable oil. This study addresses the second step when French fries are removed from the oil bath. When the potato strip crosses the oil-air interface, it lifts oil up with two possible fates, penetrating the crust or flowing along the surface or dripping at the bottom ends. The entire process was imaged at high acquisition rates (>100 Hz) and quantified by capturing each oil droplet. Oil imbibition and drainage were decoupled by comparing the results for real French fries and impervious metallic geometries. The effects of geometries and shapes were studied and used to validate a generic oil coating-dripping model coupled with our multiscale model of oil imbibition at the tissue scale (AIChE J., 61: 2329–2353, 2015). Oil uptake appears as a non-monotonic function of time. Oil is lost from the surface as 3 and 5 drops within the first seconds. Residual heat transfer and vaporization in regions fully covered by oil generate a steam film capable of destabilizing droplets. Oil thermal contraction during cooling creates an additional suction force. Numerical simulations and comparing the behaviors between pervious and impervious French fries show that oil uptake could be cut by half by improving dripping and preventing cooling and steam condensation for a short period. The main factors affecting the dripping kinetics and the possibility to deoil already impregnated products are discussed.