Revisiting the mechanisms of oil uptake during deep-frying

Abstract

Deep-frying is one of the most used and versatile technique for cooking foods. During immersion stage, it has been well accepted that the internal vaporization created an overpressure across the crust higher than the oil capillary pressure. As a result, oil could penetrate inside the food product only during the very last stages of frying or during cooling. This study shows a more complex picture in parfried frozen French fries with oil being capable of penetrating deep inside the product during the first minute of immersion. The new mechanism invokes a Carnot cycle between hygroscopic and frozen regions mediated by steam along cracks and fissures. Oil labeling and microscopic analysis show that both enthalpic and entropic forces drive oil transport and that oil can replace or be replaced by another phase: new oil, water, air. This work suggests new strategies based on thermodynamics to minimize oil pickup in fried products.