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material properties of high performance cookware.

What makes 'high performance cookware' perform? From a technical perspective, it comes down to two things: the materials used and the way those materials are combined. Read on for Ensembl's deep dive into the fascinating world of materials engineering, as we explore the properties of high performance cookware.


part one. the materials.

 

High performance cookware should be made from materials that combine high thermal diffusivity and low reactivity to produce a pot or pan that evenly distributes heat and does not react with the food being cooked. 

 

thermal diffusivity.

Cookware needs to evenly smooth out the uneven heat received from the stove’s element so that you can have the same temperature across the surface of the pan. Uneven heat will lead to hot spots across the pan, meaning you’ll have some food that is overcooked or even burnt in some places, and food that is undercooked in others.

Your cookware therefore needs to:

  1. react quickly to changes in the energy it receives (the heat), and
  2. quickly transmit the energy (the heat) it receives across the pan. 

A material’s ability to react to and transmit energy is called thermal diffusivity. Materials with high thermal diffusivity react quickly to energy received and quickly transmit the energy received  while materials with low thermal diffusivity react slowly to energy received and slowly transmit the energy received. Copper and aluminum are considered to have high thermal diffusivity while stainless steel is considered to have low thermal diffusivity.

EXAMPLE.

Low thermal diffusivity. When the pan is placed on a hot element, the area of the pan directly under the element will get really hot. The element, however, only imparts heat to the parts of the pan which are in contact with it. The rest of the pan will heat up as the energy is transmitted throughout the pan. If the pan is made of materials with low thermal diffusivity, it will take a long time for the heat to transfer to the entire pan. While the pan heats across, the burner on the stove will continue to transfer more heat to the area of the pan directly above it. This means that by the time the outer edges of the pan are “hot”, the spot directly over the burner will be “extremely hot”. The “extremely hot” parts of the pan are referred to as “hot spots”.

High thermal diffusivity. When the pan is placed on a hot element, the area of the pan directly under the element will heat up quickly and begin to transmit the heat across the pan. Because of the speed at which the heat is transmitted, the pan will have an even distribution of heat across the cooking surface.

Grilled cheese does a great job of showing the difference between cooking on a pan with high thermal diffusivity versus a pan with low thermal diffusivity.

  • Low: cooks quickly in the middle but slowly around the edges. By the time the outer cheese has melted and the edges of the bread have browned, it’s likely that the middle, especially where the “hot spots” are located, will be burnt.
  • High: browns evenly, and the cheese will melt uniformly.

thermal diffusivity

reactivity.

Great cookware also needs to be non-reactive, meaning the metal should not react with the food you’re cooking. If the material the cookware is made from reacts with the food in the pan, the taste of food can change, and chemical elements from the material may leach into the food.

Highly reactive metals include copper and aluminum. Non-reactive metals include stainless steel.

 

how to get the benefits of both.

In order to get the benefits of high thermal diffusivity materials (like copper or aluminum) plus the benefits of non-reactive materials like stainless steel, cookware should be made with layers (each layer is called a ply). You can create cookware that has stainless steel on the surfaces that comes in contact with food, then add one or more materials with high thermal diffusivity, like copper or aluminum, to the middle. In this way. the food never comes in contact with reactive materials, but the cookware has the benefit of even heat distribution across the surface.

 

the optimal combination of materials.

Based on what we've learned above, we know that we can’t get everything we want in our cookware from a single material – materials with high thermal diffusivity are reactive with foods, while materials that won’t react with foods have low thermal diffusivity. We also know we want materials that won’t rust or tarnish, and are easy to clean.

The solution is to combine multiple layers of materials: non-reactive, durable materials for the shell of a pot or pan to ensure nothing is leached into your food and the pot or pan will last, and materials with high thermal diffusivity at the core to ensure the pot or pan will be able to absorb and transmit heat evenly throughout.

Stainless steel is a great option for the inner and outer layers of a pot – it does not react with food, is not prone to rust or tarnish, and can be magnetized, meaning it can be used on an induction cooktop. So, if we’re looking to make a pot that’s easy to maintain and works on all cooktops, stainless steel is a fantastic choice for the pot’s shell.

Between the layers of stainless steel is where we want to use materials with high thermal diffusivity – this is what will ensure the pot absorbs and transmits heat evenly across the cooking surface. It’s important to note that thermal diffusivity changes by material and increases by thickness, so in order to determine how evenly a pot will heat you need to consider both the type of material and its thickness. Both copper and aluminum have relatively high thermal diffusivity compared to other metals; note that we can achieve similar results by using about 1mm of copper or 2mm - 2.5mm of aluminum.

STACKmaterialcompositiondescription

how to shop for the optimal combination of materials

It is important to call out that cookware is not typically sold based on thickness of a particular material. Instead, it is sold based the number of plies (layers).

This can be confusing because the thickness of a ply is not standardized and does not differentiate between materials. This means that:

  • the number of plies is not indicative of thickness (five layers that are 0.5mm thick is not as thick as three layers that are 1.2mm thick),
  • the impact of thickness will depend on the material used (recall from above, 1mm of copper should produce results similar to 2mm - 2.5mm of aluminum.
Therefore, the actual thermal diffusivity will be based on the material used AND its thickness!

What to make of this?

Multiple layers are important, but getting caught up in the specific number of plies is not. (Take a minute to let this sink in, as this is NOT how cookware is currently sold.)

What we want is multi-ply cookware: a thin ply of stainless steel on the outside and inside of our pot so that we have a non-reactive interior and durable exterior, and a thicker ply of copper or aluminum on in the inside so that we have evenly distributed heat across the cooking surface.

If we are using aluminum, we need a thicker layer than we would need if we used copper in order to achieve a similar thermal diffusivity.

 

part two. combining materials.

 

How do we put these multi-layers together? There are two options: we can add a multi-ply layer to the base only and use a single layer of stainless steel for the sides (disc bottom) or make the entire pot from a single, uniform sheet that combines all the metals and is multi-ply throughout (fully clad).

While it is definitely cheaper to use a disc bottom pot instead of fully clad pot (you are using less copper or aluminum, which are more expensive than stainless steel), we think the benefits of using a fully clad pot are well worth the extra costs, here’s why:

Disc bottom pots suffer from thermal discontinuity, which means the heat will be different depending on where you are in the pan. This is because the heat will be transferred quickly across the disc bottom compared to slowly across the sides. We’re therefore likely to overheat the bottom of a disc bottom pot while the top and sides remain cool. As a result, the evenly heated cooking surface is reduced, and our best cooking is limited to the bottom of the pan.

While we understand this may not always be a major concern (for example, if we’re searing a steak, or primary concern is with how even the heat is where my steak touches the pan), it can be an issue if we’re making dishes where we do want to cook on all areas of the pan, such as a stir fry, omelet, curry or tomato sauce. Disc bottom pots also run the risk of burning and scorching food at the outer edges, especially when cooking on a gas stove, as the gas pushes out to the edges and is prone to overheating certain areas.

In contrast, fully clad cookware evenly distributes heat across the entire pot – both the bottom and sides – providing an even, large cooking surface. Burning or scorching food is also less likely than with a disc bottom pot as there won’t be major temperature changes where the materials change (since there are no material changes!), and cleaning should be easier as there won’t see unexpected scorch marks.

disc bottom vs fully clad cookware heat

The bottom line:

Great cookware is going to be multi-ply and fully clad, made from a stainless steel shell and a core of either copper or aluminum. If you’re using aluminum, note that you will need to use a thicker layer than you would have had if you were using copper in order to achieve the same result.