 The hot oil heats the water within the food, steaming it; oil cannot go against the direction of this powerful flow because (due to its high temperature) the water vapor pushes the bubbles toward the surface.As long as the oil is hot enough and the food is not immersed in the oil for too long, oil penetration will be confined to the outer surface.Foods deep-fried at proper temperatures typically absorb "no more than a couple of tablespoons per cups of oil" used.