Convection oven

The first oven with a fan to circulate air was invented in 1914 but it was never launched commercially.[3]

The first convection oven in wide use was the Maxson Whirlwind Oven, invented in 1945.[4]

A convection oven has a fan with a heating element around it. A small fan circulates the air in the cooking chamber.[5][6]

One effect of the fan is to reduce the thickness of the stationary thermal boundary layer of cooler air that naturally forms around the food. The boundary layer acts as an insulator and slows the rate that the heat reaches the food. By moving the cool air (convecting it) away from the food the layer is thinned, and cooking occurs faster. To prevent overcooking before the middle is cooked, the temperature is usually reduced by about 20 °C (40 °F). In addition, because the air gets well mixed, the oven has a very even temperature.

Convection ovens may include radiant heat sources at the top and bottom of the oven, which improves heat transfer and speeds cooking from initial cold start. On the other hand, some ovens have all the heating elements placed in an outside enclosure and hidden from the food. This reduces the effect of radiant heat on the food; however, the walls of the oven will also be heated by the circulating hot air, and though the resulting temperature is much lower than that of a radiant heat source, it is still hot enough to provide some heating of the food by radiation from the walls.

A convection oven allows a reduction in cooking temperature compared to a conventional oven. This comparison will vary, depending on factors including, for example, how much food is being cooked at once or if airflow is being restricted, for example by an oversized baking tray. This difference in cooking temperature is offset as the circulating air transfers heat more quickly than still air of the same temperature. In order to transfer the same amount of heat in the same time, the temperature must be lowered to reduce the rate of heat transfer in order to compensate.

Product testing of toaster ovens has demonstrated no notable advantages to convection cooking over conventional toasting or baking.[7]

Another form of a convection oven is called an impingement oven.[8] This type of oven is often used to cook pizzas and lightly toast bread in restaurants, but it can also be used for other foods. Impingement ovens have a high flow rate of hot air from both above and below the food. The air flow is directed onto food that usually passes through the oven on a conveyor belt.

Impingement ovens can achieve a much higher heat transfer than a conventional oven, and fully enclosed models can also use dual magnetrons,[9] like a microwave oven. The most notable manufacturer of this type of oven is Turbochef. The differences between an impingement oven (with magnetrons) and a convection microwave oven are cost, power consumption, and speed. Impingement ovens are designed to be used in restaurants, where speed is essential and power consumption and cost are less of a concern.

There are also convection microwave ovens which combine a convection oven with a microwave oven to cook food with the speed of a microwave oven and the browning ability of a convection oven.[10][11][12]

A combi steamer is an oven that combines convection functionality with superheated steam to cook foods even faster and retain more nutrients and moisture.

An air fryer is a small countertop convection oven designed to simulate deep frying without submerging the food in oil.[13][14] A fan circulates hot air[13] at a high speed, producing a crisp layer via browning reactions such as the Maillard reaction. Some product reviewers find that regular convection ovens or convection toaster ovens produce better results,[15][16][13] or say that air frying is essentially the same as convection baking.[17]

The original Philips Airfryer used radiant heat from a heating element just above the food and convection heat from a strong air stream flowing upwards through the open bottom of the food chamber, delivering heat from all sides, with a small volume of hot air forced to pass from the heater surface and over the food, with no idle air circulating as in a convection oven. A shaped guide directed the airflow over the bottom of the food. The technique was patented as Rapid Air technology.[18][19]

Traditional frying methods induce the Maillard reaction at temperatures of 140 to 165 °C (284 to 329 °F) by completely submerging foods in hot oil, well above the boiling point of water. The air fryer works by coating the food in a thin layer of oil and circulating air at up to 200 °C (392 °F) to apply sufficient heat to cause the reaction.[20]

Most air fryers have temperature and timer adjustments that allow more precise cooking. Food is typically cooked in a basket that sits on a drip tray. The basket must be periodically agitated, either manually or by the fryer mechanism. Convection ovens and air fryers are similar in the way they cook food, but air fryers are generally smaller and give off less heat.[14]