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wiseGEEK:

What Is a Convection Oven?

Rather than let hot air circulate randomly, a convection oven carefully creates a uniform temperature with internal fans that evenly circulate hot air. Convection ovens are often more expensive than standard, or radiant, ovens, but they cook food faster, at a lower temperature, and often with better results. Fans ensure that the same temperature reaches the top and bottom of foods, as well as foods at all rack levels. They are also called European, true, turbo or fan ovens.

A frequent complaint of cooks with radiant ovens is that bottoms of foods get scorched, while tops are not browned evenly. This is because the temperature is not the same over the course of the cooking time, as well as over the volume of the oven cavity. A convection oven can correct this variation by using a fan that blows pre-heated air throughout the oven and around the food, rather than simply surrounding food with heated air. When air is blown onto food, it tends to cook more evenly than when it is surrounded by heated air.

Benefits of Cooking with a Convection Oven  

Saves time and energy: Because the heated air transfers heat more efficiently to cooking containers and exposed food surfaces, food will take less time to cook. Most recipes can be cooked for 25% shorter time, which ends up saving energy. The temperature at which food cooks may need to be lowered slightly on a trial and error basis.
Retains flavor: A convection oven may also do a better job at sealing in the juices of meat so dishes taste more flavorful and moist.
Cooks evenly: Baked goods, such as pies or cookies, will be more evenly browned, even if placed them on different racks. Pastries often comes out better, too, because the heat doesn't fuse the flour and butter, but allows it to form flakes.
Cooks more at once: When using multiple racks, the food itself won't interfere with the heat that reaches other foods.
Works with broilers: Most convection ovens also have a broiler, allowing food to be exposed to high heat when required.
Cooking with a convection oven requires some adjustments, such as figuring out new cook times and temperatures. Trial-and-error is the most common method of learning how to use the fan oven efficiently. Many major hardware and electronic stores sell the ovens and they can also be purchased on the Internet.