The Burning Question: Understanding Hot Pot Bottoms

When the bottom of a pot becomes hot, it is usually because it is being heated by a stove. The burner transfers heat to the pot, which in turn transfers heat to its contents. The type of stove and pot used will determine the forms of heat transfer involved. For example, if the burner is electric, most of the heat is transferred by conduction, with some heat reflected by the metal surface below the burner up to the bottom of the pot, and a small amount contributed by convection. If the burner is gas, most of the heat transfer is by convection, with smaller contributions from electromagnetic radiation and conduction.

The heat from the stove burner transfers to the pot

When you place a pot on a stove burner, you are causing heat to flow from the burner to the pot. The burner transfers heat to the pot, which then transfers heat to its contents. The process by which energy flows from the burner to the pot involves several forms of heat transfer.

If your stove burner is an electric coil, most of the heat is transferred by conduction. The heat is conducted from the burner to the pot at the points where the two are in direct contact. Because the burner emits energy in all directions, some of the energy directed downward is reflected by the metal surface below the burner (the reflector) up between the spaces of the burner coil to the bottom of the pot. This type of heat transfer is called radiation. Lastly, because the air between the burner and the reflector is hot, there is a small contribution to the heating of the pot by convection.

If your stove burner is gas, most of the heat transfer is by convection, where the burning, high-temperature gas flows along the bottom of the pot. There are also smaller contributions from the burning gas producing electromagnetic radiation in both the visible and infrared spectrums and conduction from the hot metal prongs that support the pot.

If your stove has a ceramic cooking surface, heat transfer is mainly by conduction. However, because pots tend not to be perfectly flat on the bottom, especially after some use, the pot is only in partial contact with the ceramic surface. In the narrow air spaces between the stove and the pot where there is no contact, radiation and convection contribute to the heat transfer.

If your stove has an infrared cooking surface, there are electric coils sealed below a transparent ceramic surface that emit electromagnetic radiation in the form of infrared and visible light to heat the pot. Some of the energy is absorbed by the ceramic surface, which in turn contributes to heating the pot by conduction where the two are in contact and by both radiation and convection where they are not.

If your stove is ultra-modern and has an induction cooktop, it uses none of the three aforementioned forms of heat transfer to heat the pot. With induction cooking, the "burner" uses electromagnetic induction to create eddy currents in the ferrous metal base of the pot. The metal's resistance to the eddy currents causes it to rapidly heat up. Only certain pots can be used with an induction cooking system; copper or lightweight aluminium pots will not work.

The pot's bottom becomes hotter than its sides

The bottom of a pot becomes hotter than its sides due to the way heat is conducted from the heat source to the pot. When a pot is heated, the heat is conducted from the burner to the pot at the points where the two are in direct contact. The bottom of the pot is in direct contact with the heat source, while the sides of the pot are not, which is why the bottom gets hotter.

The burner transfers heat to the pot, which in turn transfers heat to its contents. The process by which energy flows from the burner to the pot involves several forms of heat transfer, including conduction, radiation, and convection. The type of heat transfer depends on the type of burner being used. For example, if the burner is an electric coil, most of the heat is transferred by conduction. If the burner is gas, most of the heat transfer is by convection, with smaller contributions from radiation and conduction.

In addition, the shape of the pot can also affect how heat is distributed. In a tall pot with a deep level of liquid, the liquid at the bottom will be hotter than near the top, so it is necessary to stir the liquid and reposition the ingredients for even cooking. On the other hand, in a wide pot with a shallow level of liquid, the temperature of the liquid will be more constant, and the ingredients will cook more evenly.

It is important to note that the contents of the pot, such as water or food, can also affect heat distribution. For example, when water is heated, the temperature at the bottom of the pot will be warmer than at the top until the water reaches a rapid boil. At that point, the temperature of the water begins to approach equilibrium due to vigorous circulation within the water caused by bubbles moving from the bottom to the surface.

Furthermore, the presence of certain foods or liquids in the pot can also affect heat distribution and cause the bottom to become hotter. For instance, if there is not enough thin cooking liquid in the pot, the bottom of the pot can become too hot and trigger a "burn" message on an Instant Pot. Similarly, if the liquid in the pot is too thick, heat will build up at the bottom before the top starts to boil, potentially leading to a "burn" message.

The type of stove affects heat transfer to the pot

The type of stove you use will affect the way heat is transferred to the pot. There are three methods of heat transfer: conduction, convection, and radiation.

If you are using an electric coil stove, most of the heat is transferred by conduction. The heat is conducted from the burner to the pot at the points where the two are in direct contact. Because the burner sends energy in all directions, some of the energy directed downward is reflected by the metal surface below the burner, up between the spaces of the burner coil to the bottom of the pot. This type of heat transfer is called radiation. Lastly, because the air between the burner and the reflector is hot, there is a small contribution to the heating of the pot by convection.

If you are using a gas stove, most of the heat transfer is by convection, where the burning, high-temperature gas flows along the bottom of the pot. There are also smaller contributions from the burning gas producing electromagnetic radiation in both the visible and infrared spectrums, and conduction from the hot metal prongs that support the pot.

If you are using a ceramic cooking surface, heat transfer is mainly by conduction. However, because pots tend not to be perfectly flat on the bottom, especially after some use, the pot is only in partial contact with the ceramic surface. In the narrow air spaces between the stove and the pot where there is no contact, radiation and convection contribute to the heat transfer.

If you are using an infrared cooking surface, there are electric coils sealed below a transparent ceramic surface that emits electromagnetic radiation in the form of infrared and visible light to heat the pot. Some of the energy is absorbed by the ceramic surface, which in turn contributes to heating the pot by conduction, where the two are in contact, and by both radiation and convection, where they are not.

If you are using an induction cooktop, it does not use the three aforementioned forms of heat transfer to heat the pot. With induction cooking, the "burner" uses electromagnetic induction to create eddy currents in the ferrous metal base of the pot. The metal's resistance to the eddy currents causes it to rapidly heat up. Only certain pots can be used with an induction cooking system; lightweight aluminum or copper pots will not work.

The pot's contents can affect the temperature

The contents of a pot can affect the temperature in several ways. Firstly, the specific heat capacity of the contents plays a role. Specific heat capacity is the amount of heat energy in joules required to raise the temperature of one gram of a substance by one degree Celsius. Different substances have different specific heat capacities, with water having a high value of around 4 kJ/kg°C. This means that it takes more heat energy to raise the temperature of water compared to other substances with lower specific heat capacities. For example, meat has a specific heat capacity of around 3 kJ/kg°C since it is about 70-75% water. Therefore, adding meat to a pot of water will affect the overall specific heat capacity of the contents, and consequently, the rate at which the temperature changes.

In addition to specific heat capacity, the heat conductivity of the contents also comes into play. Heat conductivity refers to the rate at which heat flows through a material. For instance, a metal spoon has high heat conductivity, while a wooden spoon has low heat conductivity. When a substance with high heat conductivity is placed in a pot, it will affect how quickly heat is transferred to the other contents of the pot, thereby influencing the temperature.

Convection, or the movement of heat through a fluid due to actual motion of the fluid, is another factor that influences temperature. When solid substances are added to a pot of liquid, they can disrupt the natural convection currents in the liquid, altering the way heat is distributed and affecting the temperature.

The volume of the contents in the pot can also impact the temperature. As the volume of the contents increases, the surface area available for heat transfer may change, affecting the rate at which heat escapes the pot. This, in turn, can impact the temperature of the contents.

Finally, the order in which ingredients are added to the pot can also influence temperature. For instance, in an Instant Pot, adding starchy ingredients too early can cause them to stick to the pot and burn. This can trigger a "burn" warning, indicating that the inner pot has gotten too hot. Therefore, the sequence in which ingredients are added can indirectly affect the temperature by influencing the likelihood of burning and triggering a temperature warning.

The pot's contents can burn and stick to the bottom

The contents of a pot can burn and stick to the bottom for a number of reasons. One of the most common causes is a lack of sufficient liquid, which can cause the bottom of the pot to become too hot and trigger a "burn" message on an Instant Pot. This can also occur if the liquid in the pot is too thick, as it may not be able to generate enough steam to build pressure.

Another reason for burning and sticking is the incorrect addition of ingredients. Starchy ingredients, such as beans and rice, should be added at the correct time and in the right order, as they are more likely to stick to the pot and burn. Ingredients like dairy and cornstarch should be added after pressure cooking, as they can thicken the contents and make them more susceptible to burning.

Additionally, forgetting to deglaze the bottom of the pot after sauteing can also lead to burning and sticking. This involves pouring a thin cooking liquid, such as broth, into the pot and scrubbing the flavorful brown bits off with a wooden spoon before pressure cooking.

Furthermore, a faulty sealing ring or an improperly sealed lid can cause steam to leak, leading to insufficient liquid in the pot and potential burning and sticking.

To prevent the contents of the pot from burning and sticking, it is important to follow recipes and instructions carefully, ensure proper sealing of the lid, and maintain adequate levels of thin cooking liquid.

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