Ever wondered how to deep-fry without oil? This is almost, if not quite, the same.

Deep  frying might be the only cooking technique that seems to make  everything better, from the mundane, like french fries and chicken  wings, to the outright strange, like the fried stick of butter at the  Iowa State Fair, or fried jelly beans at the Massachusetts State Fair.

The  tragic part is that fried foods are notoriously bad for our health, but  their crunchy texture and savory flavor makes them difficult to resist.

Lucky  for us, we live in the age of the air fryer, a small kitchen appliance  that promises the same flavour and texture of deep frying, but without  all the oil and calories.

Perhaps this sounds too good to be true?

Or, you’ve achieved only mediocre results using your air fryer, which don’t quite stand up to deep fried food?

That’s  because air frying and deep frying are incredibly different cooking  techniques that yield distinct textures, flavours, and colours. To  understand why, we need to take a closer look at the physical changes  that occur in food when deep frying or air frying.

It  might come as a surprise, but frying food is actually an ancient method  of cooking, and the first written record is found in the Bible.

The  book of Leviticus, found in the Old Testament, outlines in excruciating  detail how certain sacrifices should be carried out. We are talking  intricate directions of how to properly sacrifice your cow, goat or  sheep. Or maybe a smaller animal like a bird, if you were less wealthy.

Interestingly,  frying comes into play if you didn’t have an extra animal to sacrifice:  you could do a grain offering instead. Following the instructions  outlined in Leviticus, you should pick a flour and oil of your choice.  It should be well-soaked in the oil and prepared on a griddle. Think of  little fried pieces of dough, perhaps like tiny donuts.

The directions even go on to say this shall make a pleasant aroma that can be presented to the Lord [1].

Fast  forward to the mid-1900s, and deep frying is about to have a huge spike  in popularity. A kitchen appliance salesman by the name of Ray Kroc is  about to have his big break.

Kroc  was visiting the restaurant owned by the two McDonald’s brothers, and  was so impressed that he gave up his sales career, instead purchasing  the rights to their establishment. Kroc was obsessed with the speed at  which food got to the customers and the unbelievably low prices  advertised by the brothers. He understood the potential of this business  model, the possibility of immense growth, and had huge visions for the  future [2].

For  better or worse, Kroc was integral in producing the present day fast  food industry. He realized the importance of deep frying as a method for  mass production of food.

It  was fast: not only to cook the food, but also to get out to hungry  customers. Any untrained employee could set the basket into the oil,  wait for a timer to go off, then remove the basket from the fryer. It  was cheap: the oil could be reused and you didn’t need a trained chef.  You really didn’t even need a skilled adult, a teenager would be more  than capable.

It  was Kroc’s standardized methods, almost assembly-line like production,  that led us to low skilled and low wage jobs in the fast food industry.  The success and profits achieved by Kroc fuelled many imitators giving  us the modern fast food.

In  classical deep frying that we know and love, food is fully immersed in  hot frying oil. Here, the oil acts as a heat transfer agent. Usually  held at 120–180°C (~250–350°F), or way higher than boiling water, it  warms the food and makes it safe to eat [3].

We  know that to cook food we need some type of heating medium — whether  that be an open fire, oven, or frying oil. Here, because it’s so hot  with oil touching it, the surface of the food begins to lose moisture.  The water just boils away.

So far, no problem with deep frying, right?

The  nutritional problems with fried foods begins when the frying oil starts  to act as a mass transfer agent. Any water that’s evaporated from the  food’s surface ends up leaving open pores. And what does the frying oil  do, but migrate right into these open spaces [4]!

One  study suggests that more than 40% of the final fried food is composed  of frying oil [5]. This large increase in fat-percentage is exactly what  makes them so unhealthy.

Unfortunately, that same mechanism also generates that crispy, brown crust that makes these foods so craveable.

The  inside of the food doesn’t get quite as hot as the outer surface, never  approaching the boiling point of water. That means the inner parts of  the food have minimal moisture loss — so fried foods remain juicy in the  centre, while crispy on the outside. An almost irresistible pairing of  textures.

The  unfortunate combination of suboptimal nutrition and high craveability  of deep fried foods ultimately led to the birth of the air fryer.

This  innovation is marketed as a small kitchen appliance that can be used at  home as a healthier option to traditional frying. It promises a more  nutritional versions of food, with less calories and fat, while still  retaining the texture and feel of deep fried foods — something that  previously seemed truly impossible.

Although  air fryers come in many different shapes and sizes, the internal parts  all operate on the same principles. Most come with a perforated basket  that is used to hold the food as it cooks. There are typically small  holes on the bottom of the basket and sometimes slits down the side.

Right  above the food basket, is the main heating element. If you turn your  air fryer upside down you can see this. Usually, it looks like the  spiral coils you see on stove tops. The heating element (the coil) is  placed as close to the food as possible.

Directly  above the heating element is a fan. The fan is positioned so that it  draws air up through the heating coil. As the hot air is pulled upwards,  it eventually reaches the top of the cooking chamber, and is directed  down the outer walls of the air fryer.

Once  the air hits the bottom of the air fryer, it follows a specially shaped  element that directs the air upward through the perforated basket. The  small holes in the basket allow this heat to migrate upwards as it heats  the food. Since the fan is always drawing up air, this results circular  air flow that continuously cooks the food.

The  arrangement of the heating coil and fan is key since it allows the food  to be cooked by two different heat transfer mechanisms. For anyone who  hasn’t taken a basic science class in awhile, recall there are three  main types of heat transfer: conduction, convection, and radiation. In  the case of air frying, both radiation and convection are used.

Radiation  is unique from convection and conduction since it doesn’t require  direct contact to transfer heat. Instead, electromagnetic waves are used  to warm things and radiation occurs through empty space. This is one of  the functions of the heating coil in the air fryer. It’s placed  directly above the food and heats it via radiation. This is also how the  the sun heats the earth or a campfire keeps you warm in the evening.  You can feel the heat even if you are not touching the heating source.

On  the other hand, convection uses a moving liquid or gas to directly  contact and warm substances. This is where the fan in air fryers comes  into play. The circular movement of air encouraged by the fan promotes  hot air to continuously be cycled and come into contact with the food.  This cycle or process is known as convective currents You also use  convective currents when boiling a pot of water. The bottom of the pan  is hot, and it warms up the water near it. Hot water has a lower density  than cold, therefore the hot water migrates up, forcing cooler water  down.

Finally,  conduction is when two objects are in direct contact, the hotter one  warms the colder one. If you burn your hand by placing it on a hot  stove, that’s conduction! Air fryers don’t use conduction since no  heating element directly touches the food being fried.

It’s  this combination of radiation from above via the hot coil, and  convection from below form the hot air, that gives air fried foods their  “fried” properties. When air frying, “fried” really is meant to express  that the food is heated evenly on all sides. Even if the food is piled  up, it won’t need to be turned over during cooking, similar to deep  frying.

Because  of this, the term “air frying” is a bit of a misnomer. Really, most air  fryers act more like a convection oven and the food is baked, rather  than fried.

And  if you’re confused where the oil comes in when air frying, you are not  alone. Traditionally, the word “frying” implied the use of hot fat or  oil when cooking food. However, air fryers actually work without adding  any oil. And if you do want to add oil, you have to do it before putting your food in the air fryer.

There  aren’t any special compartments to hold oil in air fryers. You can add  oil by lightly spraying the food, or using a brush to coat the food  prior to air frying — but don’t add too much! Most air fryers are made  to work best with little to no oil.

And plus, having less oil with air-frying is kind of the point.

Although air frying is really not “frying,” we do know it makes healthier food compared to deep frying.

If  you are someone who needs to see some real numbers, one study found 70%  less fat on air-fried versus deep-fried potatoes. Calorie-wise, this  corresponds to a reduction of 45 k-calories for every 100 grams of  potatoes [3]. One of the biggest issues with deep fried foods is just  how energy dense, or high in calories, these foods are while lacking key  nutrients like vitamins and minerals.

Of  course, we need some fat in our diets — but deep-fried foods tend to  provide way more than needed. So much so, that frequent eating of  deep-fried food is often studied by medical doctors for any associations  with chronic illness.

Unfortunately  for us, high consumption of deep-fried foods has been linked to obesity  [6], type 2 diabetes [7, 8] hypertension [9, 10], and heart failure  [10]. On a more morbid side, one study that followed male physicians,  saw an increased likelihood of death by cardiovascular disease  associated with eating of deep-fried food seven times or more a week  [11].

On  the bright side, all of these studies looked at people who ate  deep-fried food frequently, typically four or more times a week.

So I guess it’s still okay if I treat myself to the occasional treat.

Nutritionally,  there is no doubt that air frying beats deep frying by a long shot. But  before you go out to purchase an air fryer, let me make a few final  points.

First,  look to see if your oven has a convection mode. This would cook your  food with that same cyclically flowing air method used in air fryers,  but without spending the extra money, or making your kitchen more  cluttered. It’s also good to be aware that air frying usually takes  twice as long as deep frying, so anticipate cooking times more similar  to baking rather than frying.

If  you are someone who frequently eats deep-fried food, and don’t mind  sacrificing a little bit on taste and texture for a more balanced meal,  then air frying is for you. However, if you are unwilling to compromise  on the quality of your traditional deep fried food, the results from an  air fryer will likely disappoint you.

There is a reason we crave deep fried food, and the reason is that fat is delicious.

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