As in the original convection ovens, in an air fryer a fan circulates hot air (but it's done 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, or say that air frying is essentially the same as convection baking/roasting.

The original Philips Air fryer 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'.

Air Frying, A History:

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.

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.

In 2006, Groupe SEB introduced the world's first air fryer, under the Actifry brand of convection ovens in the French market. In 2010, Philips introduced the Airfryer brand of convection oven at the IFA Berlin consumer electronics fair. By 2018, the term 'airfryer' was starting to be used generically.

The main types of air fryer on the market today for domestic use are:

Paddle
In this type, a paddle machine moves throughout the heating chamber to move the air around more evenly. This is more convenient for the user because other types of air fryers require manual stirring throughout to ensure that all sides are fully cooked.

Cylindrical basket
A cylindrical basket is a small, single function air fryer that includes a drawer with a removable basket. A fan circulates from the top, and the food is cooked through holes in the basket. It can accommodate 2.8 litres (3.0 US quarts) of food or less on average. Because of its compact size, it preheats faster than other types of air fryers.

Countertop convection oven
Countertop convection ovens come with an air frying feature that work the same way as basket type air fryers. They usually have multiple trays or racks, so multiple things can be cooked at the same time. It holds 24 litres (25 US quarts) of food on average. They are more versatile than single function type because they have multiple features like baking, rotisserie, grilling, frying, broiling, and toasting.

Halogen
This type of air fryer cooks food with a halogen light from above. The heat is spread evenly throughout with a fan like other types of air fryers. This type usually looks like a large glass bowl with a hinged lid because the clear glass works as an easy and fast heat conductor..

How Air Fryers Work

In general, an air fryer is a countertop electrical device with adjustable time and temperature controls and a compartment, often a removable basket, that holds the food that is being cooked. The cooking process relies on a mechanism called rapid air technology, in which a heating element within the top of the machine radiates heat downward, while a fan rapidly circulates air around the food inside to heat it evenly from all angles. The air-tight, compact design of air fryers ensures that all air is contained in the chamber and actively flows around the food, promoting the intensity and efficiency of cooking. This mode of heat transfer is also known as convection, in which energy is distributed through the movement of a liquid or gaseous medium.

In an air fryer, the medium of convective heat transfer is air rather than liquid oil (as in a deep fryer), and the hot air rapidly circulating within the chamber by the action of fans is responsible for removing moisture from the surface of food. However, as air carries less heat per unit of volume compared to most frying oils, it must be moved at a faster rate to achieve the same effect as deep frying and reach the temperature necessary for the Maillard reaction to occur, 140–165°C.