Kamikaze Cookery Mythbusts: Preheated Ovens (Part 1)

[lemonrind]

The description of the heating process in an oven is only half correct. What you are describing is the conduction of heat through the air to the food, a process known as convection.

However, most of the heat used to cook food in an oven comes from infra-red radiation. The heating elements radiate heat directly into the walls of the oven, and then the walls of the oven radiate heat more evenly back into the food. The air molecules don't come into play at all.

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[lemonrind]

...continued

Preheating ensures this radiation comes from all directions evenly. Some ovens can instantly radiate even heat from its walls, so they don't need preheating. Convection ovens also don't, because they use forced hot air for even cooking.

However, most ovens do require preheating for even cooking. Otherwise you are exposing your food to a point source of infrared heat, a process known as toasting, grilling or broiling. This is fine for some foods, but it is not the same as baking.

[DanielAnchondo]

its thermodynamics with a preheated oven there is less time spent on the heat traveling into the meat and better skin doneness for the same internal temp of the meat

[DanielAnchondo]

preheated ovens work better than cold to heating up ovens for things like crispier skin on poultry without over cooking the meat and produces better physical leavening in stuff like puff pastry or pizza.