Why do we have to heat the cooking oil in a pan before frying

By | November 8, 2023

When we embark on a culinary journey, whether as seasoned chefs or amateur cooks, we often encounter the instruction to heat the cooking oil in a pan before frying. This seemingly simple step is, in fact, a crucial one that can make or break your dish. But have you ever wondered why it’s necessary to preheat the oil before you start cooking? In this comprehensive exploration, we will delve deep into the science and art of heating cooking oil in a pan before frying, uncovering the mysteries of sizzling, shimmering oil, and the Maillard reaction.


Heating the Pan and Oil

To begin our journey into the world of preheated oil, let’s first address the question of how to heat the pan and oil. It’s a fundamental concept that lays the foundation for successful frying. The importance of getting both the pan and the oil hot before introducing your ingredients cannot be overstated. This practice ensures that the food sizzles, caramelizes, and cooks to perfection.

There are two common approaches to heating the pan and oil:

Heat the Pan Before Adding Oil: Some chefs prefer to heat the empty pan first until it reaches the desired temperature. Once the pan is sufficiently hot, they add the cooking oil. This method allows for precise control of the pan’s temperature and the oil’s readiness.

Heat the Pan and Oil Together: Others choose to add the oil to a cold pan and heat both together. This method is efficient and can save time. The oil and the pan reach the desired temperature simultaneously.

Either way, the objective is to ensure that the pan and oil are scorching hot before introducing your ingredients. But why is this so crucial?


Preventing Sticking

food stick to pan

One of the primary reasons for heating the cooking oil in a pan before frying is to prevent food from sticking to the pan’s surface. The science behind this phenomenon is intriguing. Raw proteins found in meat and other food items can interact with the metal of the pan at a molecular level. This is not a mere matter of sticking in the traditional sense, where food gets trapped in microscopic cracks or pores of the pan. Even on a perfectly smooth, polished surface without any imperfections, proteins can form molecular bonds with the metal.

So, how does preheating the oil come to the rescue? Heat plays a transformative role in this culinary process. The application of heat causes proteins to undergo changes in their structure. They may fold in on themselves or even break down, forming new compounds. When proteins assume these folded or rearranged forms, they no longer exhibit a propensity to stick. Thus, the objective is to cook the food before it even has a chance to come into direct contact with the metal surface. The heated oil serves as a medium that can cook the food quickly as it passes from the air, through the film of oil, and into the pan.

In scenarios with a sufficiently hot pan and the right cooking material, the heat from the surrounding air and the radiant heat from the pan itself may be adequate to achieve this outcome. However, the presence of oil further aids in the cooking process. An alternative approach is to pre-sear meats using a blowtorch before introducing them to a hot skillet.

This is why most recipes calling for searing meat recommend heating the oil in the pan to the point where it starts shimmering or even lightly smoking. The shimmering oil is a clear indication that it has reached the temperature range of approximately 300 to 400°F, while smoking oil signifies even higher temperatures, depending on the type of oil used. The oil effectively becomes a built-in temperature indicator, providing guidance to the cook on when to commence the frying process.

It’s worth noting that there are situations where it’s perfectly acceptable to start with both the oil and other ingredients in the pan before applying heat. This approach is typically employed when the food being cooked is unlikely to stick, and a slow, even cooking process is the desired outcome. Sautéed onions, for instance, are a prime example of when this practice is suitable. Even when a recipe suggests heating the oil first, there’s often no discernible difference in the final result when this alternative method is applied.

In essence, what you truly want is “hot pan, hot oil.” Regardless of whether you heat the oil in the pan along with the food or add it at the last minute, the goal remains the same – to have both the pan and oil at the right temperature. Some cooks even prefer the technique of adding the oil with the pan to gain insight into when the pan has reached the desired heat, using the appearance of the oil as a visual indicator.

Now that we’ve explored the necessity of heating the oil in a pan before frying, let’s delve deeper into the various benefits and implications of this practice.


Enhancing Flavor and Texture

frying fish with Enhancing Flavor and Texture

Heating the oil plays a pivotal role in enhancing the flavor and texture of fried food. When the oil is hot, it facilitates the formation of a crisp and flavorful outer layer on the ingredients. The high temperature quickly seals the surface of the food, creating a desirable texture. This seal locks in the food’s natural moisture, ensuring that it remains juicy and succulent on the inside.

The Maillard reaction is a central player in this flavor and texture enhancement. It is a series of chemical reactions that occur between amino acids (found in proteins) and reducing sugars when exposed to high heat. This reaction is responsible for browning and enhancing the flavor of the food. Preheated oil aids in facilitating the Maillard reaction, resulting in the coveted golden-brown, crispy exterior on fried items.

Insufficiently heated oil can lead to the food absorbing the oil rather than sizzling in it, resulting in a less flavorful outcome.

Referring to the video below, chef Wang Gang is doing a demo of frying foods with low and high temperature oil. The foods for demo are tofu, fish, and eggplant. Frying at low temperature results with food sticking, easily breaking into pieces, and food absorbs the oil. While frying with high temperature oil results with a crispy and golden brown surface, and the food is maintained with complete shape.


Ensuring Efficient Cooking

Efficiency is another critical aspect of preheating the oil before frying. When the oil is hot, it efficiently transfers heat to the food. This means that the food cooks rapidly and uniformly. The risk of food becoming overcooked or undercooked is minimized, as the hot oil ensures that the ingredients are exposed to the right amount of heat for the optimal duration.

Efficient cooking is not only about ensuring that food reaches a safe internal temperature, but also about achieving the desired texture and flavor. Preheating the oil sets the stage for a well-executed cooking process that results in food that is both delicious and safe to eat.


Creating the Maillard Reaction

Maillard Reaction

As previously mentioned, the Maillard reaction is responsible for the browning and flavor enhancement of fried foods. Achieving the Maillard reaction is dependent on a combination of factors, with the temperature of the cooking oil being a crucial component. The Maillard reaction occurs most effectively at higher temperatures, which is why preheating the oil is vital. It sets the stage for the reaction to take place, resulting in beautifully browned and flavorful dishes.


Temperature Control

Precise temperature control is essential in cooking, and it can be challenging to achieve without preheating the oil. When you start with cold oil, it’s difficult to determine the pan’s actual temperature. By preheating the oil, you gain valuable insights into the pan’s readiness. The shimmering appearance of the oil indicates that it has reached a temperature range of approximately 300 to 400°F, and smoking oil signifies even higher temperatures, depending on the oil type. This information allows you to adjust the heat source and make any necessary modifications to achieve the desired cooking temperature.

Different recipes and ingredients may require specific oil temperatures to achieve the best results. For example, when searing a steak, you want the exterior to be exposed to high heat to initiate the Maillard reactions that result in browning and flavor development. Preheating the oil ensures that the pan is hot enough to achieve this effect. Conversely, when you want to soften ingredients like onions or garlic without browning them, it’s essential not to preheat the oil too much, as excessive heat can lead to caramelization or burning before the desired softening occurs.


Testing the Oil

The key to successful frying is achieving the right oil temperature. So, how do you know if the oil is hot enough? There are several reliable techniques to test the oil’s readiness:

Visual Cues: When you lift the pan and swirl the oil, it should behave much like water, moving quickly and fluidly. Additionally, the oil should display what can be described as “fingers” as it swirls. These “fingers” signify that the oil is stretching in places, indicating its readiness. Moreover, the oil should shimmer, showing a glistening, wavy appearance.shimmering oil on pan

Small Bubbles: When a piece of food is added to the hot oil, small bubbles should immediately appear around the food. This is a clear sign that the oil is hot enough to create the desired crispy texture.

oil bubbles while frying

The Wooden Spoon Test: If you have a wooden spoon on hand, you can use it to test the oil. Simply dip the tip of the wooden handle into the oil. If the oil starts bubbling around the wood, it’s an indication that the oil is sufficiently hot for frying. Be cautious, though, as other materials like plastic or metal may not provide this useful indicator.

oil bubbles at wooden spoon

These tests serve as reliable tools for ensuring that your oil is at the optimal temperature for frying. Achieving the right temperature is vital for a successful outcome, but what happens when the oil gets too hot and starts to smoke?


Dealing with Smoking Oil

oil smoking on pan

While heating the oil is essential, it’s crucial to avoid overheating it to the point where it starts to smoke. Smoking oil can introduce a bitter, acrid flavor to your dish and may even be a safety hazard. If your oil begins to smoke, there’s no need to panic. Here’s what you should do:

Remove from Heat: The first step is to immediately remove the pan from the heat source. This action will stop the oil from getting hotter and potentially causing a kitchen mishap.

Pour Out the Oil: Next, carefully pour the smoking oil into a heat-proof container, such as a glass or ceramic dish. This not only prevents the oil from further overheating but also preserves the oil for future use, as long as it hasn’t become too damaged by the excessive heat.

Lower the Heat: Reduce the heat on your stovetop to prevent the pan from reheating too quickly when you return it to the burner.

Start Again: Once the pan has cooled down and the oil no longer smokes, you can return it to the heat source and begin the frying process anew.

By following these steps, you can salvage your cooking adventure when the oil begins to smoke. But what are the underlying reasons for heating the oil, and why is it integral to the art of frying?



In summary, preheating cooking oil in a pan before frying is a culinary art and science that contributes significantly to the success of your dishes. It prevents sticking, enhances flavor and texture, ensures efficient cooking, facilitates the Maillard reaction, and enables precise temperature control. Whether you choose to heat the oil along with the pan or add it at the last minute, the goal remains the same: to have both the pan and oil hot, creating the ideal conditions for a delicious and beautifully prepared meal.

To conclude, next time you embark on a culinary adventure involving frying, remember the importance of heating the cooking oil in your pan. This simple yet critical step is the gateway to achieving exceptional flavor, texture, and culinary artistry in your dishes. Happy cooking!


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