How Do Deep Fryers Work? (Types, Oils, And Proper Use)

Image of a deep fryer preparing food

Deep fryers cook food in phases. In the first phase, oil is heated to a high temperature before the food is dropped into it. Next, the hot oil makes the moisture in the food vaporize and simultaneously cook the food. The food is done when all of the water evaporates, and the bubbles disappear.

While this is how all deep fryers operate, there may be slight differences according to the type of deep fryer.

Types Of Deep Fryers

We can broadly classify deep fryers as gas and electric. Apart from this classification, we can also divide deep fryers based on their structure into the following.

Tube-Style Deep Fryers

These deep fryers have heating tubes running along their base. When the heating tank is heated, the tubes transfer heat to the oil.

Beneath the tubes is a sediment area. All the crumbs, burnt food, and other residue settle into this area during the frying process. This prevents carbonization and keeps the oil fresh for longer.

The main advantage of a tube-style deep fryer is that it’s easy to clean. Since the heating tubes are separate from the rest of the tank, you can clean them easily.

Open-Pot Deep Fryers

The heating element is wrapped around the base on the exterior of the tank in these deep fryers. They can run on electricity or gas.

When the base of the deep fryer becomes heated, the oil in the pot will also become warm.

Additionally, there is a sediment zone at the bottom of the deep fryer to catch all the burnt bits.

Open-pot deep fryers usually hold large amounts of oil, making it easy to cook a big batch of food at once.

Flat-Bottom Deep Fryer

As the name suggests, flat-bottom deep fryers have a flat bottom. There is no separate area for the heating tubes, they are directly connected to the base.

So, the leftover food particles settle out of the hot oil. This type of deep fryer is best suited for bulk frying of chips and other smaller ingredients.

Pressure Fryers

Pressure fryers are generally used for commercial cooking. Their operation differs from that of standard deep fryer models because the oil is heated to high temperatures very quickly.

Pressure cooking reduces the need for oil and speeds up the cooking time. It’s typically employed in commercial restaurant kitchens to make fried chicken, French fries, and similar dishes.

Parts of A Deep Fryer

Most deep fryers will be made of stainless steel. Let’s look at the other parts of this appliance.

Heating Element

The heating element is usually in the base of a deep fryer. It’s usually in direct contact with the oil and transfers heat to the oil.

Oil Reservoir

The oil reservoir is the big pan that holds the cooking oil. As we mentioned earlier, it’s typically constructed with stainless steel.

The oil reservoir should be deep enough to fully immerse the food items during cooking. It should also not be overfilled to prevent spilling and accidents.

Frying Basket

The frying basket allows you to lower the cooking ingredient into the oil without directly dropping it into the oil.

When the food is lowered into the oil, bubbles appear around it. When it’s done, you can easily lift the basket with the cooked food.

It’s much easier than having to fish out the cooked food after frying.

Electronic Components

Electric deep fryers will have several electric and electronic components. This includes:

  • A control panel with buttons or dials to adjust the temperature, set the cooking time, and other cooking functions.
  • The thermostat maintains a constant cooking temperature and prevents the oil from overheating or underheating.
  • Overheating protection circuits act as safety features to prevent accidents and fires due to overheating of the oil.


Most deep fryers have a lid to keep the appliance closed when it’s not in operation. It’s usually not required during the deep-frying process.

However, it helps to prevent splatters when cooking large or moist ingredients.

Oil Drainage System and Sediment Tray

Deep fryers hold large amounts of oil. However, you may not need so much oil to fry a single batch of food.

But burnt food or crumbs in the oil will contaminate the oil that remains, reducing its quality.

To prevent this, advanced deep fryers usually have an oil drainage system and sediment tray. They catch and separate the food residue from the oil, making it convenient to reuse the oil.

Depending on the make and model, deep fryers may also have other parts like a viewing window, cool-touch handles, and automatic shut-off controls for safe operation.

How Do Deep Fryers Operate?

Deep frying is a process in which the food is cooked in hot oil at a temperature of 325°F to 400°F.

At this temperature, the food cooks and develops a crispy exterior. Technically, there are four phases to this process.

  1. Heating: When you switch on or apply heat to the deep fryer, the oil in the container starts heating up. Once the oil reaches the right temperature, you can add the food into the basket and place it in the oil. The sudden exposure to heat will immediately cook the exterior surface of the food. Meanwhile, the insides are still uncooked. The crisp outer coating seals the moisture inside the food.
  2. Surface Boiling: During the second phase, the oil is still hot, which causes the moisture inside the uncooked food to vaporize. As the water evaporates, it cooks the insides of the food. You will notice bubbles at the food surface during this time. They are formed when the evaporating water touches the hot oil. These bubbles prevent the oil from getting inside the food.
  3. Reducing Heat: As cooking progresses, the water in the food gets used up. The bubbles on the surface will also begin to disappear.
  4. Bubbling Stops: When the bubbles disappear, it means that all the moisture in the food is over, and it is properly cooked. You should now remove the food from the deep fryer. If you leave it in for any longer, it will start absorbing oil as there is no bubble shield anymore.

Step-by-Step Process to Use a Deep Fryer

Here is the sequence of steps to follow when using a deep fryer

1. Choose the Right Type of Oil

A deep fryer uses high heat. Hence, it’s ideal to use cooking oils with a high smoking point to prevent them from breaking down during deep frying.

You can use vegetable oil, canola oil, coconut oil, peanut oil, or animal fats like butter or lard for frying.

However, oils like peanut oil and coconut oil can impart their flavor to the cooked ingredients.

Once you choose the correct oil, add it to the oil reservoir before turning on the heat. This will prevent it from splashing and causing burns.

Additionally, follow the indications on the deep fryer when filling the reservoir. Avoid exceeding 2/3rds of the oil reservoir to prevent accidents.

2. Turn on The Deep Fryer

To turn on the deep fryer, there should be a switch. The device should also have controls for the heat setting. Choose from low, medium, or high as per your need.

In the case of a gas fryer, heat the stove and adjust the flame.

Close the lid of the deep fryer while the oil heats to speed up the process.

3. Check the Temperature

The deep-frying temperature for most foods is between 325°F and 375°F. If the deep fryer has an inbuilt thermostat, it will stop heating the oil beyond this temperature.

You can also use an oil thermometer to test the temperature.

Keep an eye on the oil while it’s heating. The presence of smoke indicates that the air fryer has overheated. Turn down the heat if you notice any smoke.

4. Drop the Food Into the Basket and Immerse It in The Deep Fryer

Food in deep fryer

Once the oil is hot, you can deep fry the prepared food. However, moisture on the food surface can make the oil splatter and splutter.

To prevent this, pat the food dry before putting it in the oil. Dab it with a kitchen towel before placing the ingredients in the food basket and lowering it into the oil.

The food will start bubbling on all sides. These bubbles are caused by the moisture in the food that evaporates.

As it evaporates, it will also gently cook the food on the inside. This is why deep-fried food has a crunchy crust and soft interior.

5. Fry Till the Food Turns Golden Brown

When you deep fry food, the food first cooks on the outside, forming a crust. The crust locks moisture, which turns into steam and cooks the inside of the ingredient.

The crust browns during the cooking process and becomes golden brown over time.

There are two factors to look for to identify when the food has cooked properly:

  • The outside turns golden brown, and
  • The bubbles around the food disappear because all the moisture in the food evaporates.

When you notice both these factors, you can take the food out.

6. Gently Lift the Basket and Transfer the Cooked Food

Remove the food from the deep fryer by lifting the basket slowly. You can transfer it to a drying rack to pat off the excess oil with a paper towel.

At this stage, the insides of the food will be extremely hot. So allow it a few minutes to cool down before serving.

Here are a few things to remember while removing food from a deep fryer:

  • The right time to retrieve the cooked food is when the bubbles disappear. Lift the basket gently and shake it well to get rid of the excess oil.
  • Place the food on a drying rack or paper towels and let it cool down a bit before use.
  • Wait till the oil properly cools down to drain the inner pot and clean the deep fryer. Keep the lid on while it cools. Make sure it is out of the reach of children or pets, as hot oil is dangerous and can cause accidents.

7. Wait for The Oil to Cool to Discard or Store

After frying, turn off the deep fryer and wait for the oil to cool completely before handling it. It can take an hour or two for the oil to cool.

After this time has elapsed, either transfer the oil to a container for later use or discard it in the trash if it can’t be reused.

Interesting Further Reading: Can A Deep Fryer Explode? (What Causes Explosion + How To Avoid It)

The Importance Of Choosing The Right Type Of Oil

When choosing an oil for deep frying, the main aspect to consider is its smoking point.

The smoking point is the temperature at which the oil breaks down.

When the oil reaches this temperature, it becomes unstable.

If you further increase the heat, it will break down and release harmful toxins.

Since deep frying involves heating of oil to a very high temperature, choose an oil with a high smoking point.

It will allow you to safely heat the oil to the temperature mentioned in the recipe.

Canola oil, coconut oil, and peanut oil are good for deep frying. Some oils, like coconut oil, have a strong flavor.

So, you may also like to consider this factor if you do not want the flavors of the food to be affected.

Always use the right amount of oil.

Avoid filling more than half of the container, as the oil may spill and lead to accidents.

Use the level indicator inside the deep fryer as a guide.

Additionally, pour the oil only when the deep fryer is turned off and cool.

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