Understanding Pan Structure

In the discussions on Understanding Pan Metals, I noted the rates of heat transfer in different metals called the "thermo-conductivity coefficient." It gives the calories of heat that the metal transfers over a centimeter of length in one second, measured in the metric system (Celsius). The rates for the commonly used metals in pans are as follows. The higher the number, the greater the speed of heat conductivity.

Copper .94
Pure Aluminum .53
Cast Aluminum .33
Steel .16
Cast Iron .12
Stainless Steel .05

Using the following mathematical formula, the optimum thickness for even distribution of heat within a pan's interior surface, so that hot spots are avoided, can be calculated.

thickness of metal  x  thermo-conductivity coefficient = 2.65 (THERMCO)

The optimum thickness for metals most commonly used for pans is as follows:

Copper 2.82 millimeters
Pure Aluminum 5 millimeters
Cast Aluminum 8.03 millimeters
Steel 16.56 millimeters
Cast Iron 22.08 millimeters
Stainless Steel 53 millimeters

It is for this reason that Mauviel and Bourgeat both make copper pans that are 2.5 to 3 millimeters thick, and Sitram, Mauviel, Bourgeat, and Demeyere all make stainless steel pans with a 5 millimeter or thicker aluminum thermo-conductive base.

What does this mean for particular kinds of pans used in a kitchen?

Most Pans
Most pans only need a thermo-conductive base. That is because heat need only come at the food from the bottom.

This is obviously true of fry pans, sauté pans, and rondeaus (low casseroles). But it is also true of saucepans, stew pots, and stock pots. Thermo-conductive sides in such pans actually waste heat by moving it up the sides where it radiates into the air around the pan. Thermo-conductive sides also add unnecessary weight and expense to the pan.

Pan w/ Thermo-Conductive Core

However, solid copper pans and solid aluminum pans are made by pressing the metal into shape, and thus the sides are as thick as the base. It is the efficient way to make such pans, regardless of the lack of need and extra weight for cooking purposes.

It is a different matter for stainless steel pans and cast aluminum pans. Stainless pans are pressed and a thermo-conductive base attached. As heat moves into the pan interior, the stainless steel, being a poor conductor, keeps it in the pans for efficient cooking. Cast aluminum pans are molded so the base is thicker than the sides.

Slow Cooker, Stove Top Oven
A (1) slow cooker, such as made by Demeyere - 2.5 millimeter aluminum core, (2) stove top oven, such as made by Le Creuset, or (3) special buffet casserole and stew pot, such as made by Mauviel in the Induc'inox line, all have medium thick thermo-conductive bases and sides. This is because the intent is to get heat coming at the food from all directions, as in an oven, even though used on a burner. Also, since the food is cooked at a low temperature for an extended length of time, the metal does not have to be optimum thickness to avoid hot spots. The low temperature is also the reason carbon steel and cast iron can be used: the metals gradually heat up and hold the heat for slow, lengthy cooking. Le Creuset's unique feature is the heavy cast iron lid which heats up slowly but (1) radiates significant heat down at the food and (2) maintains a higher pressure in the pot which cooks the food a bit faster. The Demeyere slow cooker has a .

Le Creuset Pot w/ Thermo-Conductive Lid

Saucier
The saucier functions similar to a slow cooker. It cooks a sauce at a relatively low temperature. For even cooking, it is best if the heat comes at the sauce from both the bottom and sides. Thus, Demeyere makes its sauciers with an aluminum core going through the base and up the sides with a thickness of 2 millimeters for small sauciers, and 2.3 millimeters for large ones. Mauviel's Induc'inox splayed saucepans serve the same function with a thermo-conductive carbon steel core going through the base and up the sides.  Every All-Clad pan is constructed on the optimum principle for a saucier pan.

Wok, Stir Fry Pan
Hot spots are not a major problem for woks even though high temperatures are used in cooking. This is because the food is (1) constantly stirred, (2) oil is used for deep-frying, or (3) water is used for steaming. Moreover, it is desirable to have a significant heat difference between the base and sides when stir-frying. This is so cooked foods can be moved from the base to the sides to keep warm, but not continue cooking, as other foods are put in the bottom to begin cooking or left in the bottom for further cooking. For this reason, carbon steel woks work well. Demeyere uses a 1.3 millimeter aluminum core in its woks; it is thick enough for good heat conductivity in the base, but preserves the heat difference in the sides (not too little, but not too much heat in the sides).

Fish Poachers
Because both water and a low temperature are used in poaching, hot spots are not a problem. You do not need a thermo-conductive base.

Roasting Pans and Roasters
Because ovens bring gentle heat to a pan from all directions, neither a thermo-conductive base nor sides are needed. You just need a pan that will not warp. If you bring the pan from the oven to a burner to deglaze it, since you will be using water and stirring constantly, hot spots are not a problem.

Demeyere and Mauviel
Only Demeyere makes pans with different optimal thermo-conductive structures to fit the function of the pan. That is one reason it is our benchmark pan. Mauviel makes two different lines of pans - Pro-inox and Induc'inox - which have different thermo-conductive structures. Pro-inox pans have an optimally thick thermo-conductive base; Induc'inox has a thick thermo-conductive core.