Have you ever noticed that the center of your frying pan seems a little elevated?
It’s not a mistake or a coincidence—it’s actually a result of the way pans are made and how they react to heat.
In this article, we’re going to explore the science behind this curious phenomenon.
We’ll take a closer look at the impact of sudden temperature changes, the uneven way heat is distributed, and how the size and quality of your pan can all contribute to the pan’s distinctive shape.
By the end of this article, you’ll have a clearer understanding of why pans rise in the middle, and you’ll see that there’s a lot more to your kitchen cookware than meets the eye.
Table of Contents
Why are pans raised in the middle?
The metal undergoes temperature shocks due to rapid temperature changes in localized regions at the base of the pan. This leads to expansion or contraction when the metal rapidly heats up or cools down, resulting in areas on the pan bottom lifting or bulging. Certain pan designs feature a concave base to counteract metal expansion and prevent warping.
The rapid change of pan temperature causes warping.
Rapid temperature fluctuations can lead to warping in pans.
Such fluctuations can occur when a pan is exposed to extreme heat followed by sudden cooling, or when it goes from extremely cold to being subjected to high heat.
For instance, consider the scenario where a pan has just finished cooking and is still hot.
If it is immediately exposed to cold water, the sudden temperature change can have adverse effects.
When the hot metal of the pan comes into contact with the cold water, it undergoes contraction.
However, this contraction is not uniform across the pan’s surface.
As a result, the pan experiences uneven thermal stress due to this sudden temperature variation, which ultimately leads to warping.
It’s important to note that the extent of this warping is influenced by the magnitude of the temperature difference.
The greater the difference between the initial and final temperatures, the more pronounced the thermal shock will be, and consequently, the higher the likelihood of warping occurring.
Uneven Heating and Hot Spots.
The distribution of heat across a cooking stove is not uniform, particularly when it comes to induction stoves.
On the hob, the center tends to be hotter than other areas where the pan is placed.
This discrepancy in temperature arises from the fact that metal directly above the heating elements heats up more quickly than its cooler surroundings.
However, this heated metal encounters a limitation in its horizontal expansion and instead expands vertically, thereby leading to the warping of the pan.
Consequently, placing a pan on a stove set to high heat at the beginning of cooking can result in the pan warping.
This phenomenon is more likely to occur if the pan is constructed from a material with low thermal conductivity or if the heat source is centralized at the hob’s center.
Referring to the above photo by J. Kenji López-Alt from reddit, it is a thermal imaging photo capturing various types of pans heated over a gas burner for 90 seconds, the carbon steel and cast iron pans develop hot spots over the burner rings. Carbon steel & cast iron have relatively lower thermal conductivity compared to other materials like copper.
The uneven expansion and stress can lead to the pan’s base warping or buckling.
This warping alters the pan’s initially flat surface, which, in turn, can lead to instability during cooking and unevenly cooked food.
Mismatched Stove Burner Size with the Pan.
The size of your pan and its quality are also factors that contribute to the rising center.
Stove hobs are engineered to achieve even heat distribution across their entire surface.
When a pan that doesn’t fit the stove hob size is used, a particular area of the pan’s base receives more heat than the rest.
The concentration of heat in specific spots causes these areas to expand more rapidly than the cooler portions, creating an imbalance of stress on the pan’s base.
If you use a pan that’s too small for the burner, parts of the pan don’t get the heat they need.
This can cause some areas to expand more than others, creating stress and eventually causing the pan’s center to rise.
Same as well for pan size bigger than the burner, the edges of the pan will not get the heat, causing uneven heating and end up pan warping.
The Influence of Pan Quality (thickness)
The quality of a pan significantly influences its susceptibility to warping.
When a pan with a thin base is placed on a stove and heated, it can develop areas of high heat concentration, often referred to as hot spots.
These localized zones of intense heat can result in uneven expansion of the metal, ultimately leading to warping.
This expansion prompts the material to bend and distort, consequently causing warping.
Thin materials lack the robustness and structural integrity that thicker ones possess.
In comparison to pans with thicker bases, those with substantial thickness exhibit enhanced stability and rigidity, thus displaying superior resistance to warping.
Thicker pans demonstrate a greater ability to maintain their original shape when subjected to heating.
Their increased mass facilitates more uniform heat dispersion across the cooking surface, mitigating the occurrence of concentrated hot spots that tend to induce warping.
In situations where a pan experiences rapid heating or cooling, the variance in expansion and contraction between different sections can induce warping in thinner pans.
Thicker pans, due to their inherent resilience, remain more resilient to thermal shocks.
Moreover, the durability of thicker pans makes them well-equipped to endure repeated cycles of heating and cooling without succumbing to warping.
Conversely, thinner pans may gradually deform over time, particularly if exposed to high temperatures or sudden temperature fluctuations.
Tri-Ply and Multi-Ply Pans have good resistance against warping.
Tri-ply or multi-ply pans are composed of three or more layers of metal that are intricately bonded together.
Typically stainless steel, aluminum, and copper.
Each metal layer has different thermal conductivity properties.
Aluminum and copper are exceptional heat conductors, adept at minimizing hotspots and diminishing the likelihood of warping, they expand more due to their high thermal expansion rates.
In contrast, stainless steel layers, with their lower expansion rates, experience more modest expansion.
As the pan heats up, layers with higher thermal expansion rates (such as aluminum or copper) undergo more pronounced expansion, while layers with lower expansion rates (like stainless steel) expand more conservatively.
The external stainless steel layers, effectively counteract the expansion of the inner copper or aluminum layers.
The outer stainless steel layers play a balancing role, curbing overall expansion to a controlled extent.
Due to the bonding of these materials, internal stresses naturally arise within the pan when subjected to heat are evenly distributed across the entire pan’s structure.
By promoting balanced stress distribution, the risk of warping or distortion during heating and cooling cycles is significantly diminished.
Soft Metals Mechanical Stress
Pans crafted from a single layer of soft metal material are susceptible to warping and cracking over time.
Metals like aluminum and copper, known for their softness, can contribute to the deformation of pans due to their reduced rigidity and vulnerability to mechanical stress.
When such a pan is placed on an uneven heat source—be it a gas burner or an electric stove top coil—and does not uniformly cover the base, certain sections of the pan will experience more direct heat compared to others.
Consequently, these specific areas will become notably hotter, resulting in the creation of localized hot spots, gradually resulting in the elevated center.
The Pan Designed with Concave in the Base.
Given that metals naturally expand when subjected to heat, the potential for warping of the pan’s bottom base exists.
To counteract this, pan manufacturers often opt for a concave design in the base, anticipating the inevitable expansion.
This curvature not only accommodates the expansion but also ensures that the pan maintains a stable and secure position on the stove, particularly when handling high-temperature frying.
Despite these deliberate deviations from absolute flatness, these design considerations tend not to compromise the overall functionality of the pans, even when used with induction or radiant stoves.
Now that you know the science behind pans raising in the middle, your cooking adventures can be even more fascinating. It’s not just about creating delicious dishes—it’s also about understanding the materials and physics that make it all possible.
Armed with this newfound knowledge, you can take steps to maintain your pans’ integrity. To keep your pans flat and stable, consider the following:
Choose Quality Pans: Opt for thicker pans made from a combination of materials to ensure better resistance against warping.
Match Pan Size: Always use a pan that matches the size of the burner to ensure even heat distribution.
Moderate Heat: Start with medium heat before cranking it up. This allows for gradual expansion and reduces the risk of sudden warping.
Avoid Extreme Temperature Changes: Avoid exposing a hot pan to cold water or vice versa, as rapid temperature changes can lead to warping.
Handle Soft Metal Pans with Care: If using pans made from soft metals, be mindful of heat distribution and avoid exposing them to high heat.
Invest in Multi-Layer Pans: Consider upgrading to tri-ply or multi-ply pans, which offer enhanced stability and better resistance against warping.
With these steps, you can continue crafting culinary delights with pans that remain steadfast and true, defying the temptation to rise and warp.