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The Relationship Between Heat Transfer and Cooking

Have you ever wondered how food becomes hot as you prepare it in your commercial kitchen equipment? While this is something we usually take for granted, the science behind how our food becomes piping hot and safe to eat - known as heat transfer - is both complicated and fascinating. Keep reading to learn more about the relationship between heat transfer and cooking and the important role it plays in your commercial kitchen.

What is Heat Transfer?

Put simply, heat transfer is the process of an item or substance coming into contact with a heat source and becoming hot. In more scientific terms, heat transfer is an exchange of thermal energy between two objects. The rate of heat transfer depends upon the temperatures of each entity (i.e. burner and saucepan) and the medium through which the thermal energy is being transferred.

How is Heat Transfer Used in Cooking?

Heat transfer is a very important aspect of the cooking process. Heating food destroys potentially harmful bacteria and other microorganisms, which makes food safe to eat and easier to digest. When food or liquids become hot, their molecules absorb energy, begin vibrating rapidly, and start to bounce off of each other. As they collide, heat energy is produced and transferred, which warms and cooks our food.

Methods of Heat Transfer

There are 3 types of heat transfer:

  • Conduction
  • Convection
  • Radiation

Each of these methods features its own unique characteristics, but there is also some crossover between the different types.

What is Conduction Cooking?

Conduction cooking is the process of heat being transferred between objects through direct contact. For example, the electric burners on commercial stoves will conduct heat energy to the bottom of a pan sitting on top of it. From there, the pan conducts heat to its contents. Your deep fryer also cooks foods in this manner, as oil has a high rate of heat conduction. Because it's responsible for moving heat from the food's surface to its interior, conduction occurs when cooking with convection and radiation methods, too.

Conduction is the slowest method of heat transfer, but the direct contact between the cooking surface and the item to be heated allows food to be cooked from the outside in. When grilling a steak, for example, conduction produces an evenly cooked exterior and a moist, juicy interior that guests are sure to love.

Examples of Conduction Cooking

Here are a few examples of how heat transfer via conduction works:

  • Touching a burner on a stove and being burned
  • Grilling steak, chicken breasts, or pork chops
  • Using ice water to blanch vegetables after steaming to keep them from losing their color

What is Convection Cooking?

Convection combines conduction heat transfer and circulation to force molecules in the air to move from warmer areas to cooler ones. As the molecules closest to the heat source become warm, they rise and are replaced by unheated molecules. There are two types of convection.

Natural Convection

Natural convection occurs when molecules at the bottom of a cooking vessel rise and warm while cooler and heavier molecules sink. This creates a circulating current that evenly distributes heat throughout the the substance being prepared. For example, when a pot of water is placed on the stove to boil, conduction transfers heat from the pot and into the water molecules in contact with the interior of the pot. As these molecules heat, convection causes them to move away from the interior of the pot as they are replaced by cooler molecules. This continuous current creates convection heat transfer within the water.

Mechanical Convection

Mechanical convection occurs when outside forces circulate heat, which shortens cooking times and cooks food more evenly. Examples of this include stirring liquid in a pot or when a convection oven uses a fan and exhaust system to blow hot air over and around the food before venting it back out.

Examples of Convection Cooking

Here are a few examples of how heat transfer via convection works:

  • Water coming to a boil and circulating in the pot
  • Running cold water over frozen food, which transfers heat into the food to thaw it more quickly
  • Room temperature air moving around frozen food to thaw it

What is Radiation Cooking?

In the world of cooking, radiation is the process where heat and light waves strike and penetrate your food. As such, there is no direct contact between the heat source and the cooking food. There are two main radiant heat cooking methods: infrared and microwave radiation.

Infrared Radiation

Infrared radiation utilizes an electric or ceramic heating element that gives off electromagnetic energy waves. These waves travel in any direction at the speed of light to quickly heat food, and are mainly absorbed at the surface of whatever you're preparing. Examples of things that create infrared radiation are glowing coals in a fire, toaster ovens, and broilers.

Microwave Radiation

Microwave radiation utilizes short, high-frequency waves that penetrate food, which agitates its water molecules to create friction and transfer heat. If you're heating a solid substance, this heat energy is transferred throughout the food through conduction, while liquids do so through convection. Microwave heat transfer usually cooks food faster than infrared radiation, as it is able to penetrate foods several inches deep. Keep in mind that microwave radiation works best when cooking small batches of food.

Examples of Radiation Cooking

Here are a few examples of how heat transfer via radiation works:

  • Warming your hands over a fire
  • Lying in the sun to get warm
  • Heating up dinner in the microwave

Whether you're using a pan on a stove, a convection oven, or a heavy-duty microwave, conduction, convection, and radiation are all around us. If you own a catering company, buffet, food truck, or any other foodservice business, understanding the process behind heat transfer will help you make your signature dishes even better.

Posted in: Kitchen & Cooking Tips | By Nora Fulmer
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