How does an air fryer work? A fan circulates hot air at high speed which cooks the food.
Firstly, let’s look at how food cooks when it is fried. With deep-frying, food is submerged in oil that is heated to between 177 and 191˚C. That seems pretty hot, but it is far below the boiling point of cooking oil. It is extremely dangerous to reach the boiling point of oil, and probably impossible because oil will reach a smoke point and then a flash point before it actually boils. At the smoke point, which is 211˚C for sunflower oil, the oil will begin smoking profusely, then, at the flash point, which is 319˚C for sunflower oil, the oil vapor above the oil will burst into flames.
When the food is immersed in the hot oil, the water contained in the surface of the food starts to boil. The heat from the hot oil penetrates into the food and starts to heat it up. The water evaporates and rushes out of the food into the oil. The bubbles that you see when frying are not bubbles in the oil because it is far from its boiling point, they are bubbles of steam caused by the water in the food evaporating. That is also why the oil spits. The steam has more energy than the water and wants to expand. As soon as it is free of the confines of the thick oil, it explodes out, flicking hot oil with it. Frying is considered an unhealthy way of cooking but if food isn’t fried for very long, it doesn’t absorb much oil. The water vapor leaving the food has too much energy and the oil cannot go against it. However, if it is fried for too long, the food dehydrates and can absorb more oil.
When the water vapor leaves the food, free fatty acids form on the surface and a crust of starch forms. The heat cooks the inside of the food and softens the fibers, modifies the molecular structure of the proteins, and caramelizes the starches. This is known as the Maillard reaction (this is what makes toast brown) and it gives the food a rich flavor. Foods are usually covered in a starch before they are fried, such as batter or breadcrumbs, so that it forms a crust and locks in the water vapor, keeping the food moist. Foods that are heavy in starch, such as potatoes and noodles, don’t need extra starch.
So, how does an air fryer work? Food is placed in a basket and the air fryer uses a heating element to raise the temperature of the air inside the machine to 200˚C. A fan then circulates the hot air around the fryer. Because the air is circulated, it stays at a constant heat and cooks the food evenly. An air fryer is basically a convection over in a small pot. It’s possible to cook many things, but you can’t cook everything that you would deep fry. Wet batters and soft doughs drip straight through the basket.
The idea behind air frying is that it is healthier than deep frying because it doesn’t use oil. That is not necessarily true, though. Firstly, as we saw, if food is not fried for very long, the water vapor escaping from within it stops the food absorbing much oil. The oil cooks the outside of the food and as the water vapor escapes it leaves small holes that the oil can creep into. As the food is cooked for longer, the number of holes increases and the amount of water decreases, letting in more oil. However, it is pretty easy to blot this off with paper towels. Using a low gluten flour, like a rice flour, because it doesn’t absorb as much oil.
Secondly, the idea behind deep frying being unhealthy because fat is unhealthy is not true. Fat is not unhealthy. Without fat in our diet, we will die. Fat aids cell growth, protects our organs, and helps with nutrient absorption. And oils can be a great source of fat. However, not all oils are created equal. Refined vegetable oils are pretty bad for you. They have been linked to a lot of diseases and obesity. On the other hand, oils like olive oil have many health benefits. If you don’t fry your food for too long, don’t eat fried food too often, use an oil like olive oil, and fry healthy foods rather than processed foods, then frying is not very unhealthy. And this is what I learned today.
Sources
https://en.wikipedia.org/wiki/Deep_frying
https://en.wikipedia.org/wiki/Air_fryer
https://www.thespruceeats.com/how-does-an-air-fryer-work-4693673
https://www.usnews.com/360-reviews/home-goods/air-fryers/how-does-air-fryer-work
https://latourangelle.com/pages/what-does-smoke-point-mean
https://cooking.stackexchange.com/questions/86048/does-oil-boil-just-like-water-does
https://www.centrafoods.com/blog/edible-oil-smoke-flash-points-temperature-chart
https://www.doctorkiltz.com/is-vegetable-oil-bad-for-you/
https://www.everydayhealth.com/news/best-worst-oils-health/