Learn the science behind:
Every few years there seems to be a new gadget on the market that everyone raves about. A few years back the InstantPot seemed to be everywhere, and of course, don’t forget about sous vide cooking. We tend to be a little late to the game, so we’re already way behind on another of those trends: the air fryer.
Only recently did we purchase a (used, because why buy it new?) air fryer. We wanted to test the hype, but also figure out what an air fryer really is. Is it a fast oven, a deep fryer, or just something completely different? We didn’t really know so decided to dig in.
What is an air fryer?
Air fryers were developed to replace deep fryers. However, seeing how people use their air fryer online, it has clearly become more than that! People grill, bake, fry, heat, prep, all sorts of food in their air fryers. It’s fun to see how people have made air fryers their own, but, it does make it a little confusing for air fryer newbies. So, what really is an air fryer?
What is an air fryer made of?
Despite it having ‘fryer’ in the name, there’s no (or barely any) oil involved. Really, an air fryer is a small, compact, well-insulated, very efficient, convection oven with very similar components. The only component that makes it look more like a deep fryer is the little basket, but more on that later.
First, the outside. Most air fryers are stand-alone, portable units. The units are compact and well insulated. When turned on, the outside remains cool to the touch (though best not to touch it) except for some hot air coming out. The fact that they’re so well insulated is important. Our air fryer has ‘only’ 1425W power and still manages to heat up to high temperatures very quickly.
Even though the air fryer itself is quite small, the heating elements are actually huge compared to the size of the overall equipment. The top half of the air fryer contains a large heating spiral. Notice just how large it is compared to the overall air fryer size. Now have a look at your ‘regular’ convection oven. The air fryer clearly has a higher “heating element:food quantity” ratio! What’s more, the heating element sits very close, right on top, of the food which you add in the bottom half.
Above that large heating element sits a fan. This fan pulls air from below (from your food), through the heating spirals. It then pushes it back down along the sides, pulling it back through the food from the bottom. This creates some very efficient air circulation. Manufacturers claim that the special ridges at the bottom of the air fryer help optimize this airflow.
In between those special ridges at the bottom and the large heating element is where you place your food. There are all sorts of accessories for air fryers, but we’ll just focus on the basic one: the basket. It’s what makes it somewhat related to a ‘regular’ deep fryer. The bottom of the basket is full of holes, to pull the air through the food within the basket. The sides are closed, to ensure the food flows past the basket.
The circulating air is what will ‘fry’ your food (more on that below). As such, it’s crucial for the air to be able to flow closely past your food. It’s why manufacturers will tell you not to stack your food too much.
Note: we tested a Phillips brand air fryer. That said, almost all air fryers work in a similar fashion, though the designs might be slightly different. Almost keep in mind that ‘air fryers’ are trendy at the moment. In our opinion, there are a lot of toaster ovens that are now also called air fryers that truly are toaster ovens. A big difference between these two is that super optimized air flow in air fryers, instead of just bottom and top heating or a small little fan in ‘conventional’ ovens.
Heats up very quickly
An air fryer heats up really quickly. In our experience faster than both an oven (although some modern ovens heat up rather quickly as well) as well as a deep fryer. In our case, the air fryer heated up to its setpoint (200°C, which is its max) within 4 minutes! Again, this is possible probably thanks to that large heating spiral and very fast circulating air.
How does an air fryer work?
An air fryer is great at quickly moving really hot air past your food. This is what makes an air fryer ‘special’ (though not for all applications it’s that ‘special’). The air brings heat to the food and by moving past so quickly it can do so despite the fact that air itself can’t hold onto a lot of energy (it has a low heat capacity).
The fast-moving air has another role aside from heating up the food, it can also transport moisture away. The heat evaporates water in your food and the air that flows by takes this along. A good air fryer has great internal air circulation but also a way to ‘refresh’ its air to get rid of that excess moisture. If not, it wouldn’t be able to dry out your food.
Drying out the food is important if you want to make crispy crunchy food! Your food becomes crispy thanks in part to moisture being driven off.
Air Fryer vs. Deep fryer
An air fryer was designed to replace a deep fryer. Does it actually do that?
What really does a deep fryer do?
To know whether it does, we need to have a closer look at a deep fryer and see what happens when deep-frying your food. A deep fryer can be a dedicated piece of equipment, or simply a pan on a stove filled with oil. All you need to ‘be’ a deep fryer is a container of some sort filled with oil that’s heated and kept at a more or less constant temperature.
To deep-fry your food: pre-heat the oil and add the to-be-fried food into it. The hot oil quickly sears the food and cooks it, often in a matter of minutes. There are a few characteristics of deep fryers that make them ‘unique’.
1. It’s hot!
First of all, it’s hot! Oil in a deep fryer is heated to temperatures well above the boiling point of water (100°C/212°F at sea level). Typically you’d fry at 160-180°C (325-350°F). These high temperatures ensure that:
- It is easy to evaporate moisture. This is essential if you want to make your food crispy. The crispiness is a result of there only being a little bit of moisture left in the food.
- Chemical reactions happen fast. The most common example: the Maillard reaction which causes browning of your food.
- Your food heats up quickly.
2. High heat capacity
Oil has a high heat capacity compared to air. This means that one gram of hot oil contains a lot more energy than the same weight of air (and keep in mind that 1 gram of air takes up a lot more space than 1 gram of oil). As such, relatively small amounts of oil can transfer a lot of energy into your food. This energy is necessary to heat up your food and ensures all those chemical reactions can take place.
3. Sears a batter almost instantaneously
As soon as you drop a batter-coated piece of fish or vegetable in your deep fryer, the outside layer of the batter gets cooked. The heat and the presence of oil surrounding the batter help to keep it in place.
Compare this to placing a battered piece of fish in the oven. Your batter will have dropped off long before it has a chance to set. There’s nothing to hold it in place while it’s cooking. This is not the case in a deep fryer.
4. It’s oily
A deep fryer relies on oil to transfer energy and cook your food. Of course, this means there’s a lot of fat present. This has its pros and cons.
First of all, a positive effect: these fats can participate in various chemical reactions, actually improving the flavor of the food. The type of fat you use influences just exactly what happens (e.g. ghee is known to influence flavor differently than let’s say canola oil).
A disadvantage for many is that the use of fat will result in food that contains more fat. To what extent this is an issue probably depends on how often you eat fried food, but it also depends on your frying technique. It’s known that certain frying methods don’t result in as much of an increase in fat content of the food as others do.
Lastly, the fat in deep fryers has a tendency to get smelly. This is especially the case if fat has been reused a few times. Over time, the fats will oxidize and turns slightly rancid. This rancidity, as well as the general ‘fried air’ smell, are characteristic of hot fats.
Does an air fryer fully replace a deep fryer?
Even though that fat has a lot of advantages (e.g. high heat capacity, can be heated to high temperatures), there are some clear disadvantages (e.g. smell and nutritional value) as well. As such, there clearly is an interest to find a replacement. It’s tricky though to find an alternative to all of those above-mentioned functionalities of an air fryer.
In our opinion the air fryer can’t fully replace a deep fryer. There are some clear instances where the air fryer runs short. However, there are also plenty of applications where it works just fine. We’ll highlight a few based on what we tested so far.
Main shortcoming: no liquid batters!
Want to make kibbeling (battered fried fish), jalebi, or tempura? You’re out of luck with an air fryer. The air fryer can’t handle those liquid batters. The batter will seep through your basket before it has time to set. In order for batters to work, they need to be seared almost immediately. An air fryer can heat quickly, but not quick enough for those!
That said, if you’re ‘frying’ using a dry coating (like a flour coating) the air fryer seems to work just fine. We do feel it does less of a good job to really create a crunchy outside than a deep fryer, but you can still get a good mix of crunchy outside and juicy within.
Great for: pre-cooked foods
Have pre-made chicken nuggets, kroketten (a Dutch specialty), pre-made crispy chicken, pre-cooked then frozen French fries? All of these work just as great in an air fryer as they do in a deep fryer. Since the outer coating has already been ‘sealed’ the air fryer shines. Here the air fryer can do what it’s best at: heat up food quickly and create a crispy outside.
French fries for instance are commonly made by frying them twice. The air fryer is a great replacement for replacing the second fry (not so much in replacing both frying steps in one go though)!
Air fryer vs. Oven
Even though the air fryer was developed to replace a deep fryer, a quick online search taught us that it definitely isn’t used just to replace a deep fryer. On the contrary, it seems to be used as a power-charged oven!
This does make a lot of sense, seeing what we just discussed when disecting the air fryer. It does have a lot of similarities to a ‘regular’ convection oven. Both use air to heat up the food. The air fryer is just a little better at moving that air around and heating it up.
We haven’t tested all application yet, but there’s quite some evidence online that baking cakes, cupcakes and more all work well in an air fryer. Since an air fryer works very much like a ‘regular’ oven that doesn’t surprise us too much. If you have a very large oven at home, and just want to bake something small, the air fryer is probably a great alternative. Same if you don’t have an oven at all of course :-).
This is probably more microwave than oven territory, but it’s something that an air fryer is great at! When you reheat leftovers that were previously crunchy an oven has a tendency to dry it out (and just take a long time). The microwave on the other hand can make it all really soggy. A microwave heats up water molecules but is not great at making crispy food. The air fryer is the perfect in-between here! It heats up reasonably fast, and keeps the outside crispy (in our experience even making it more crispy)!
So, what is an air fryer? It’s a fast heating, efficient, oven great for heating up food quickly and giving it a crunchy crust. It’s not a deep fryer but can replace a lot of its functions. The same for the oven replacement, it can do a lot, but not everything. In other words, it’s its own unique device, useful and great for some, less added value for others.
If you’re into freshly made tempura, you can skip the air fryer. However, if you regularly make fries from frozen fries it’s a great choice :-).
Any other questions you have about what air fryers do and why they do/don’t work? We’d love to hear!
All tests were done with a Philips Viva air fryer, regular size
Angela E. Newton, Flavour formation in ghee, 2013, link
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