Deep-Frying: Boiling Food from Within

You'd think fried foods—submerged in boiling-hot fat—would be soggy in the middle, but they aren't. Read on to discover the science that makes deep-frying possible.

Despite cooking while submerged in vats of bubbling oil, deep-fried foods always seem protected from grease on the inside. Crisp french fries somehow maintain a fluffy interior, and the meat of a fried chicken breast magically retains its tenderness within the crunchy skin. The reason for this is simple: water and oil don’t mix. When pieces of potato, cod, or candy bar enter a deep fryer, the oil—so long as it’s hot enough (usually 345–375 degrees)—almost immediately boils the water within the food, forcing it to escape to the surface. As the moisture leaves the food, the vapor subsequently repels the oil, preventing it from touching anything but the outer edges.

Of course, there would be little to prevent those outer edges from getting soggy were it not for the shield of starch that surrounds most fried foods. Potatoes are naturally starchy, which is why they can fry with little preparation, but other foods—such as meat, fish, or whole pizzas—must be coated in breadcrumbs or batter before entering the oil. Since fried foods continue to steam even after frying, an ideal coating should allow the steam from inside to escape, lest it begin to sop up the remaining moisture. For this reason, fried foods should be served while they’re still steaming to ensure the crispiest outer crust.