Understanding Stovetop Cookware- Samuel Lloyd Kinsey
Explanation of how to select quality cookware and the materials of construction....
Posted 07 August 2003 - 01:22 PM Understanding Stovetop Cookware By Samuel Lloyd Kinsey (slkinsey) In various discussions about cookware over the years, I have found that many people care passionately about their cookware -- be it All-Clad, heirloom cast iron, heavy copper, or Calphalon -- but don’t really understand their cookware. This article, I hope, can be a first step towards transforming you into the equipment geek I know is lurking inside. Or at least helping you make some informed choices the next time you decide to buy a new pan. As you may imagine, this course requires no ingredients and no equipment - only some patience and a few minutes of reading time Whenever considering a new piece of cookware there are 5 basic questions you should ask yourself. 1. What kind of cooking task do you want to do? As it so happens, there are different pan designs for just about every cooking task one is likely to encounter. For example, if you want to make sauces, you would be well-advised to acquire a saucepan. An understanding of what you want to do can inform your decisions on many different levels. For example, if what you really need is a 3 quart pan for boiling water, there is no reason to spend big money on a fancy pan. 2. What is the basic pan shape? Are you buying a sauté pan? a saucepan? a stock pot? Different pan designs lend themselves to different cooking tasks, and also to different uses and deployments of materials. 3. What materials are used? Cookware materials can be differentiated by two considerations: reactivity and thermal properties. Reactivity is fairly simple. Some materials are more reactive than others, which means that they tend to react chemically with foods and produce undesirable results. Thermal properties, into which we will delve in greater detail below, include things like: How fast does it heat up? How even is the heat? How much heat does it hold? And things like that. 4. How are the materials deployed? This comes down to basic design philosophy: Is it a diskbottom design or is it straight gauge? Is it fully clad, interior lined or all one metal? 5. How much of the various materials are used? This seems like an easy thing to understand, but it is frequently overlooked. For example, a pan with a 2 mm thick aluminum base will perform differently from one with a 7 mm thick aluminum base, just as a 2 mm thick copper pan will perform differently from a 2.5 mm thick copper pan. The real trick, though, is understanding the difference between 2 mm of copper and 4 mm of aluminum.
What Kind Of Cooking Task Do You Want To Do
This seems like a relatively simple question, but it is an important one. When you are thinking of getting a new piece of cookware, don’t think “I want a new skillet.” Rather ask yourself, “what do I want to do that I cannot do with the cookware I already own? Why? What is it about my cookware that does not allow me to do what I want?” Sometimes it may be something as simple as wanting a skillet that doesn’t have hot spots. Other times it may be more complex... Maybe you want a small pan for making delicate sauces like Hollandaise and mounting reductions with butter. Then, you have to ask yourself what it is, exactly, that might make a pan good at performing these tasks. In this instance, you would want a pan that had absolutely even heat, that responded immediately when you adjusted the flame up or down, that was able to maintain its temperature when cold ingredients were added, that conducted heat into the sauce from all sides so everything was exactly the same temperature, that had a relatively large surface-area-to volume ratio for efficient reduction and that was nice and wide at the top so it was easy to get in there with a whisk. In short, you might want a stainless-lined heavy copper sauce pan, or for a little less money, a stainless lined heavy aluminum pan, or for a little less money, a stainless pan with a copper bottom. A big part of this article will be working to build a basis for understanding why, exactly you would want a sauce pan and what, exactly, would be gained and/or lost moving from a stainless lined copper pan to a stainless lined aluminum pan to a stainless pan with a disk bottom. What Is The Basic Pan Shape? This section will provide concise descriptions of the various pans used in the kitchen. Sauté Pan (Sauteuse; also Curved Sauté Pan and Slant-Sided Sauté Pan): This pan has a large cooking surface and short straight sides that are approximately one quarter the diameter of the pan. The large cooking surface provides ample contact with the heat and the straight sides help contain ingredients as they are flipped around inside the pan to brown them evenly on all sides. A long, high handle helps the cook agitate the pan for even more movement. This is what it is to sauté. The French verb “sauter” means “to jump” -- so foods that are “sauté” are “jumped around in the pan.” A lid allows the addition of liquids to sautéed items for a quick braising. The Curved Sauté Pan and Slant-Sided Sauté Pan are similar, with the refinements implied by their names. Cast Iron Skillet: This traditional pan is similar in configuration to the Sauté Pan, having a large cooking surface and short straight sides. But this is where any similarity ends. Cast Iron Skillets have short handles perpendicular to the base of the pan, and the sides are even lower -- from 20% of the pan’s diameter all the way down to 14%. As a result, they are not particularly well suited to sautéing as the ingredients would tend to jump right out of the pan. Where Cast Iron Skillets excel is in providing constant high heat for things like browning large cuts of meat, shallowfrying chicken and, of course, making cornbread. Seasoning can make these pans relatively stickresistant for cooking eggs and other such notoriously sticky foods, but the straight sides make it difficult to get a spatula in there (a better alternative is probably a nonstick pan or a purposedesigned “French steel” pan). One word about seasoning and high heat cooking: if the pan gets too hot, it will burn the seasoning and damage it. For this reason, it is useful to keep an unseasoned cast iron skillet around for extra-high-heat cooking. A common variant of the Cast Iron Skillet, and a good candidate for an unseasoned cast iron pan, is the Cast Iron Grill Pan. This is a Cast Iron Skillet with ribs extending upwards from the bottom to mimic a grill. Another
common variant is the Cast Iron Chicken Fryer, which has taller sides -- around one third the diameter of the pan. Whether this is actually a good design for frying chicken is a matter of some debate. Fry Pan: This pan is similar to the Sauté Pan with its large cooking surface and short sides. However, the fry pan has even shorter sides and they are sloped outwards to allow maximum dispersal of steam so food items fry “dry” for an optimally crisp surface. These pans are designed to quickly fry ingredients in a small amount of fat -- specifically, ingredients that are “flat” and therefore (or for other reasons) do not need to be, or should not be, sautéed.
Rondeau (Braiser, Casserole, Low Casserole): This is a low, wide, double-handled pan. The sides are right around one-third as tall as the diameter of the pan. This can be a very versatile pan for tasks as diverse as browning bones to poaching delicate meats and fishes. The lack of a long handle means it won’t take up much stovetop real estate, and it goes easily from stovetop to oven. The two major variants (not that all manufacturers stick to the same nomenclature) are the Casserole and the Low Casserole, which have sides that tend to be higher or lower than those of a Rondeau. A Casserole is essentially a large saucepan with two loop handles instead of one long handle, while a Low Casserole is essentially a sauté pan with two loop handles instead of one long handle. Another variant on this theme is the high end Paella Pan, such as those manufactured by Sitram and Paderno, which has deep curved sides and a thick conductive base. Enameled Cast Iron Casserole (Cocotte, French Oven, Dutch Oven): This is a specific kind of Casserole that deserves special mention due to its design. The enamel lining makes the pan nonreactive, while the extra heavy, thick layer of cast iron provides even heat for long, low braising and simmering. These come in both round and oval shapes, the latter being especially useful for braising large pieces of meat on the bone. An interesting traditional variant is the Doufeu, which has ribs or nodules on the interior surface of its lid. The lid is deeply indented so that it may be filled with ice water, which encourages internal vapors to condense on the ribs or nodules and drip back into the braise. A truly traditional Dutch Oven is raw cast iron, rather than enameled, and occasionally footed for use over coals. Stock Pot: This is a pot designed for making stocks. The shape is tall and narrow to limit evaporation, with sides approximately equal to the diameter of the base. This design allows stocks to be simmered a long time for maximum flavor extraction and minimal loss of liquid.
Stock pots at around 12 - 18 quarts make excellent vessels for boiling pasta with the addition of a Pasta Strainer Insert.
Saucepan (Low Saucepan): This is a pan for making sauces and reductions. The sides are traditionally half as tall as the diameter of the pan, which provides a large surface area for fast evaporation. The low sides provide easy access to a whisk for making roux and mounting sauces. Also useful in the larger sizes as a general purpose pan for blanching/steaming vegetables, reheating liquids, etc. Tall Saucepan (High-Sided Saucepan, Saucepot, Saucepan): Otherwise similar to the Low Saucepan, but the sides are taller in proportion to the diameter of the pan -- around 75%. As a result, the Tall Saucepan does not encourage fast evaporation like its shorter brother. Rather, this pan is best suited for warming/reheating sauces, soups, stews and other liquids in situations where additional reduction is not desired. Due to its proportionally greater volume, the Tall Saucepan is more useful than its shorter brother as a general-purpose pan for blanching/steaming vegetables, reheating liquids, etc. Sauteuse Evasée (Slant-Sided Saucepan, Windsor Saucepan, Sauteuse Conique, Conical Sauteuse, Fait Tout, Chef’s Pan, Reduction Pan): This is a saucepan that has been optimized for reductions. The sides are angled out from the base to provide 25% more surface area for evaporation. In addition, the sides are even lower than those on a Low Saucepan -- usually onethird as tall as the diameter of the pan. Due to its geometry, which is neither particularly high nor particularly low, the Sauteuse Evasée may be used for sautéing in the larger sizes, and the smaller sizes can be very useful in place of a Low Saucepan. Such versatility has conferred upon this pan the name “Fait Tout,” which means “does everything.” (Note: Le Creuset makes a nontraditional “Windsor” that has slanted sides, but is relatively tall and narrow. This pan does not have the same performance characteristics as the traditional designs.) Curved Sauteuse Evasée (Curved Sauteuse, Saucière, Sauteuse Bombée, Saucier, Chef’s Pan): As the name suggests, this pan is otherwise similar to the Sauteuse Evasée, only with curved rather than straight sides. In smaller sizes, the curved sides provide easy access to every corner of the pan with a whisk or spoon for sauce making. In larger sizes, the curved sides facilitate onehanded tossing of the food when sautéing.
What Materials Are Used? As previously discussed, cookware materials differ in two important qualities: reactivity and thermal properties. Reactivity Materials that are highly reactive tend to have chemical reactions with other substances around them. A good example would be iron, which tends to react with oxygen to form iron oxide or, as we commonly know it, rust. This is significant to cooking because there are certain ingredients and certain ways of cooking in which it is disadvantageous to have a reactive cooking surface because the ingredients will react with the cooking vessel and produce undesirable colors and/or flavors. Highly reactive cookware materials include iron, copper, aluminum and carbon steel. Nonreactive cookware materials include stainless steel and enamel. A special case is anodized aluminum, which is aluminum that has been treated with an electrolytic process to create a harder surface that is still somewhat reactive, but significantly less so than untreated aluminum. Similarly, a process called annealing is used to turn reactive carbon steel into harder, less reactive black steel and blue steel. As it so happens, materials that are highly reactive also tend to have highly desirable thermal properties (and vice-versa), as we will see below. Thermal Properties Thermal properties refers to those aspects of a material that have to do with heat. So, before we begin, perhaps we should have an understanding of what heat and temperature are. In all substances above absolute zero there exists a certain amount of movement in the atoms or molecules that make up that substance. This is a kind of kinetic energy, which is a fancy physics term used to refer to the mechanical energy a body has by virtue of its motion. Temperature is a measure of that kinetic energy. The greater the kinetic energy -- i.e., the faster the particles are moving -- the higher the temperature reading will be on the thermometer.
Heat is a little more difficult to nail down. In the scientific sense, it is a measure of the amount of energy transferred from one object to another because of the temperature difference between those two objects. In other words, if you put a cold object down on top of a hot object, the energy that is transferred from the hot object to the cold object would be measured as heat. Heat is not, strictly speaking, a word that describes the energy contained inside an object -- it is only a word that describes the energy exchanged between the two objects. The energy an object possesses due to its temperature -- let's say the sum total of all the atomic vibrations in an object -- is properly called Internal Thermal Energy. All that said, laypeople commonly understand “heat” to include both “heat as transferred energy” and “heat as internal thermal energy,” and that is the usage I will employ in this article. So, how does heat make it from the burner at the bottom of your pan through to the other side and into the food? The answer is: Conduction. As Harold McGee says: Quote When thermal energy is exchanged from one particle to a nearby one by means of a collision or a movement that induces movement (through electrical attraction or repulsion) the process is called conduction. Though it is the most straightforward means of heat transfer in matter, conduction takes on different forms in different materials. For example, metals are by and large good conductors of heat because, while their atoms are fixed in a latticelike structure, the outer electrons are very loosely held and tend to form a free-moving “fluid” or “gas” in the solid. This same electron mobility makes metals good electrical conductors. But in nonmetallic solids like ceramics, conduction is more mysterious. It seems that heat is propagated not by the movement of energetic electrons -- in solids of ionic- or covalent-bonded compounds, the electrons are not free – but by the vibration of individual molecules or of a portion of the lattice, which is transferred to neighboring areas. This is a much slower and less efficient process than electron movement, and nonmetals are usually referred to as thermal or electrical insulators, rather than conductors. *** As we have seen, heat conduction in a solid proceeds either by the diffusion of energetic electrons, or by vibration in crystal structures. A material whose electrons are quite mobile is likely to donate those electrons to other atoms at its surface: in other words, good conductors are usually chemically reactive. But inert compounds, by the same token, are poor conductors. Ideally we would like to have a pan that provides even heat, that is able to hold a lot of heat and that responds promptly to changes in the heat source. These three things all depend on two properties of the materials used in the pan: thermal conductivity and heat capacity. Thermal Conductivity is a physical property that describes how fast a given material can move heat around. Materials with good thermal conductivity are able to transfer heat from one part of the pan to another very quickly and efficiently, which provides even heat. The graphics below illustrate how thermal conductivity affects evenness of heat.
This illustration shows how heat, applied to a single point, is conducted through an infinitely thick piece of metal in an arbitrary unit of time (say, one second or one minute). As we can see, when we look at the highly conductive material, the material within the area we are considering is all about the same temperature. On the other hand, the less conductive material is nice and warm close to the heat source but is rather cool out towards the edge of the radius. This is because the highly conductive material was able to take the heat from the single heat source and distribute it throughout the area very quickly. The less conductive material just can’t move the heat as fast, and so was not able to move much heat to the outer areas during the space of our arbitrary unit of time. Let’s take a look at how this would work in a pan:
This illustration shows how the same single source of heat is conducted through a piece of cookware. Note that the highly conductive cooking surface is more or less all the same temperature, whereas the less conductive cooking surface is warmer in the middle and cooler towards the outside. That warm part in the middle is the dreaded hot spot -- the same thing that creates a burnt ring on the bottom of the pan when you cook a long-simmered tomato sauce. But, you may well ask, what if we just leave the less conductive pan on the heat for a longer period of time? Wouldn’t the edges eventually warm up? Good question. Let’s take a look:
This illustration shows how much heat the less conductive material can distribute through an infinitely thick piece of metal when you leave it on the heat longer than the arbitrary unit of time we specified above (say, 3 seconds or 3 minutes). As we can see, heat is conducted a much greater distance from the heat source, which we would expect given the greater interval of time. If we look at the original radius of the area we examined at first, we can see that the temperature at the edge of that area is just about the same as it was in our original unit of time for the highly conductive material. Great, you say, all we have to do is heat the less conductive material a little longer and it’s the same thing. Not so fast. Let’s have a look at how it would work in a pan:
This illustration shows how the same single source of heat is conducted through two pieces of cookware made of the less conductive material when it is left on the heat longer than our original arbitrary unit of time. As we can see, the cooking surface with the same thickness we used in the earlier example is hotter overall, but the center of the pan is still significantly hotter than the edges of the pan -- a hot spot. The thicker cooking surface, on the other hand, has a fairly uniform distribution of heat at the top where the food would be making contact. In fact, the distribution of heat and temperature at the top appears to be quite similar to what we were getting from the highly conductive material in our original arbitrary unit of time. So, what does this all tell us? It tells us that the thickness of cookware materials is important, and that less conductive materials can potentially provide even heat just as well as more conductive materials but the less conductive materials must be thicker and it will take more time for the pan
to come up to temperature. The issue of time is an important one, and brings us to the second effect of thermal conductivity: responsiveness. Responsiveness refers to a material’s ability to respond to changes in the heat source. I think we have all experienced the phenomenon of turning the heat off under a cast iron skillet only to have the meat continue to sizzle and cook as though nothing had happened. This is because cast iron does not have good thermal conductivity and a cast iron pan is not able to respond to the decrease in the heat source by cooling off quickly. When considering responsiveness, it is useful to imagine the cookware as a bucket of heat with faucets dumping heat into and draining heat out of the bucket.
In this illustration, thermal conductivity is illustrated by the size of the faucets. The highly conductive material is able to move heat from the heat source into the cookware rapidly because it has a large faucet dumping a lot of heat into the heat bucket. The less conductive material doesn’t move heat from the heat source into the cookware nearly as efficiently, so the size of the faucet is smaller. Looking at the illustration, it becomes apparent that the highly conductive bucket will fill up with heat faster than the less conductive bucket. Another way of stating this is that the highly conductive material is able to respond more quickly to an increase in the heat source by filling up with heat and getting hotter -- it is more responsive. The faucets on the bottom of the heat buckets demonstrate that the same principle works in the opposite direction. The highly conductive material can also quickly drain heat out of the bottom of the heat bucket -- by conducting the heat into the food, into the air, into water, etc. -- and respond to changes in the heat source by cooling off quickly. The less conductive material, with its smaller faucet, is once again not able to respond as rapidly. The graphic below gives the thermal conductivity for several common metals used in cookware (as well as a couple of others you will recognize, just for the sake of comparison). From a purely technical standpoint, the thermal conductivity of a material changes depending on the temperature of the material, so these numbers are not strictly true for all temperatures. That said, the relationship between the various materials remains roughly the same no matter what the temperature, so these numbers are a good indication of the relative conductivity of these materials.
As we can see, copper has by far the best thermal conductivity, with stainless steel having very poor thermal conductivity. This is why copper provides such even heat, while stainless steel is notorious for hot spots. You may refer to this chart for data on the thermal conductivity of other elements. Of note is the fact that all the materials used for cookware have pretty good thermal conductivity overall. Copper has the second best thermal conductivity of all elements, and even iron -- which we normally think of as being fairly sluggish in this regard -- has better thermal conductivity than 80 other elements! The foregoing information leads us to an interesting conclusion: that more conductive materials are able to conduct heat more efficiently into food compared to less conductive materials. This supposition is borne out in the following experiment: Start with two pans of approximately the same size/thickness, one of cast iron and the other of copper. Place both in a high oven and preheat for an hour (this will ensure that both pans have accumulated approximately the same amount of heat). Now, open the oven door, take two approximately equal steaks (or chops or similarly massive cuts of meat) and drop one into each of the two pans. Wait five minutes, remove the steaks and examine the browned side. You should notice that the steak in the copper pan is more browned than the steak in the cast iron pan. Cut into each steak and you should find that the steak in the copper pan is more cooked through than the steak in the cast iron pan. This is because the copper pan, due to having better thermal conductivity, was able to conduct more of its accumulated heat into the steak than the cast iron pan. This all assumes, however, that the cast iron pan and the heavy copper pan were holding the same amount of heat in the first place, which is the reason it was important to choose pans of approximately the same size and thickness… which leads us to the second important thermal property: Heat Capacity Thus far we have mostly been talking about heat in its pure scientific sense: as it relates to the transfer of thermal energy. Now, we will turn out attention to the second meaning of heat, as it relates to internal thermal energy. Every object -- for our purposes, every chunk of metal -- can not only be described as being at a certain temperature, but also as holding a certain amount of heat. For example, if we have a one pound piece of iron and a five pound piece of iron, both at 200 degrees C, it doesn’t take too much thinking to wrap our minds around the idea that the 5
pound piece of iron is holding more heat than the smaller piece. This is easily understood by nothing more than the fact that it had to sit on the stove a lot longer before it came up to temperature. A more scientific experiment would be to drop each piece of iron into equal sized containers of water and measure how much the temperature of the water goes up in each container. If you do this experiment, you will find that the water in the container with the large piece of iron is significantly warmer than the water in the container with the smaller piece. This is because the large piece of iron stores more heat than the small piece, even at the same temperature. As it turns out, various materials differ in their ability to store heat. In other words, some materials can hold more heat at a given temperature than others. For example, a one pound chunk of aluminum holds a lot more heat than a one pound chunk of copper at the same temperature. The scientific term that quantifies a material’s heat storage capabilities is called Specific Heat. Specific heat is the amount of heat it takes to raise one unit of a substance by one degree. The most common way specific heat is expressed is the amount of heat, measured in Joules it takes to raise one gram of a substance by one degree Kelvin, or: Joules per gram per degree Kelvin (J/g K). That said, you may also see specific heat expressed as British thermal units per pound per degree Fahrenheit (Btu/lb F) or calories per gram per degree Celsius (cal/g C) and so forth depending on the measurement system used. We’ll stick with good old J/g K for this article. Confused yet? It gets even more complicated. We also need to settle on a reference standard. Specific heat is not an absolute measurement like a meter or a kilogram. A meter is an absolute quantity -- something that is a meter long is a meter long and something that is two meters long is twice the length of a meter. Temperature systems, on the other hand, work differently. Take the Celsius scale, for example... the values of 1 and 100 are arbitrarily set at the freezing and boiling points of water. Why? Why are there 100 units between the freezing and boiling points of water? Is 20C twice as hot as 10C? How? Well, as it so happens, water has an unusual ability to hold a lot of heat, so scientists have arbitrarily designated the specific heat of water as 1. Thus, all specific heat measurements are given relative to the specific heat of good old H2O. The illustration below lists the specific heat values for the most commonly used cookware materials.
As we can see, aluminum has a very high specific heat indeed – over double that of iron. This
would lead us to conclude that a one pound chunk of aluminum holds more heat than a one pound chunk of iron at the same temperature. But wait... cast iron is supposed to hold the most heat, right? Yes and no. It is true that the chunk of aluminum holds more than the chunk of iron, but we haven’t accounted for the density of the materials. The illustration below shows the density of the same materials.
OK... now we can see that iron is a lot more dense than aluminum. A one pound piece of aluminum would be almost three times the size of a one pound piece of iron. Since cookware is described in terms of its thickness (i.e., the volume of the materials rather than the weight) it is more useful for us to understand the heat carrying capabilities of a given volume of metal rather than a given mass of metal. To obtain these figures, we can simply multiply the specific heat by the density to arrive at specific heat per cubic centimeter.
Now the picture looks completely different, doesn’t it? Aluminum is way down there on the bottom, iron and copper are in the middle, and steel is up at the top. These are much more useful numbers that more accurately reflect the way materials are deployed in cookware. A understanding of these numbers can take us a long way towards understanding the difference between a 3 mm thick aluminum bottom and a 7 mm thick aluminum bottom -- also between a 3
mm thick aluminum bottom and a 2 mm thick copper bottom. This is because we can use these numbers to understand the Heat Capacity of various cookware. Heat Capacity is the term we will use to describe the total heat holding capabilities of an entire piece of cookware. For example, if we have an 11 inch sauté pan with a 7 mm thick aluminum bottom, we can calculate the heat capacity of that base. If I plug in a radius of 14 centimeters (half of the 11 inch diameter) and a height of .7 centimeters into this handy online calculator we get a volume of 431 cubic centimeters. Multiplying that by the specific heat per cc number from above, we get an overall heat capacity of 1043. Now let us compare this aluminum bottom to a copper bottom at 2.5 mm. The volume of the copper bottom is much smaller -- only 154 cubic centimeters. Using the number for copper from above, we arrive at an overall heat capacity of 531, or around half that of the aluminum bottom. This may seem fairly esoteric, but in fact we have just used materials data to compare a 67 dollar Sitram Profisserie sauté pan with a 7 mm aluminum base to a 140 dollar Sitram Catering sauté pan with a 2.5 mm copper base. What does this tell you? It tells you that you’re better off buying the cheaper pan if you want a sauté pan with a high heat capacity so you can dump a whole bunch of stuff into it all at the same time. A good way to conceptualize heat capacity is to return to our “heat bucket” illustration from above.
The illustration above shows the difference between two otherwise similar cooking vessels made with different amounts of the same material. Because they are made from the same material, the thermal conductivity (as illustrated by the size of the faucets) is the same. As we can see, the pan made with more material has a larger heat bucket and is able to hold more heat at a given temperature -- it has a larger heat capacity. All that said, we come to the final piece of the puzzle: integrating heat capacity and thermal conductivity. As we look at the illustration above we can’t help but notice that the heat faucets are the same size, meaning that the thermal conductivity was the same for the two cooking vessels being compared. This means that the vessel with the smaller heat capacity will come up to temperature -- "fill up with heat” -- more rapidly than the vessel with the larger heat capacity. But, as we can recall from the illustration up in the thermal conductivity discussion, the size of
the faucet is not always the same. Some materials have better thermal conductivity than others.
The illustration above demonstrates the interaction of thermal conductivity and heat capacity. Here we have three cooking vessels with different thermal conductivities and heat capacities: low/high, high/high and low/low. With a little thinking, we can understand that the low/high pan will take longer to heat up and will be less responsive than the high/high pan. However, if we take the low/high pan and use a smaller amount of the low conductivity material, we reduce the thermal capacity and make it into a low/low pan. Now, if we compare the high/high pan and the low/low pan, we can understand that they will fill up with heat right around the same time. The faucet is smaller for the low/low pan, but it also has a much smaller bucket to fill up. The high/high pan and the low/low pan are equally responsive. But, there may be a price to pay... The only way to reduce the thermal capacity of the low conductivity pan is to use less of the low conductivity material. How is this done? It is done by making the pan thinner. This is important because, as demonstrated way back in the section on thermal conductivity, when the low conductivity materials become thinner there is a cost to be paid in evenness of heat. The low/low pan may be as responsive as the high/high pan, but it may also have hot spots. These are the tradeoffs that one must deal with when designing cookware. It is always a constant compromise to design a pan that has a large enough thermal capacity so it won’t lose all its heat when food is added to the pan, is thick enough to provide even heat and yet is also responsive to changes in the heat source. One last bit of science... There is a quality that nicely quantifies the relationship between a material’s thermal conductivity and its specific heat. This is called Thermal Diffusivity and it reflects what actually happens when heat is applied to a material To arrive at this number we divide thermal conductivity by density multiplied by specific heat.
Looking at this illustration, it would seem that copper is the best material among those commonly used for cookware. And, indeed it is the case that copper is theoretically the best performer in most cooking applications. However, copper is expensive and heavy, and there are many cases where other materials may be just as good or even better. We’ll come back to this later.
How are the Materials Deployed There are several overall design philosophies that can be implemented in cookware. Take a saucepan, for example. A saucepan may be made of thin stainless steel, it may be stainless steel with a conductive base of either aluminum or copper, it may be raw aluminum, it may be aluminum with an interior lining of stainless steel, it may be fully clad aluminum with stainless steel on the inside and the outside, it may be heavy copper with an interior lining of stainless steel, or it may have another design. Below we will take a look at the various designs that are commonly used for stovetop cookware. Aluminum - As we know, aluminum has good thermal conductivity, and aluminum pans provide even heat when the cookware is sufficiently thick. Thickness of materials is also important for heat retention because aluminum has relatively low specific heat per cubic centimeter. - Highly reactive with both acidic and alkaline foods, which can cause off flavors and colors. - Often warps as a result of high heat cooking. - Soft and prone to scratching. - Light. - Inexpensive. - Common uses: Almost every pan in the kitchen is manufactured in raw aluminum. Due to its reactivity, it is best used in cooking tasks where the food is neither too acidic nor alkaline and will spend a relatively brief time in the pan. - Representative manufacturers: Wear-Ever Anodized Aluminum
- This is aluminum that has been treated by an electrolytic process which makes the outer surface both harder and less reactive. Otherwise similar to raw aluminum. - Can be incredibly difficult to keep clean. - Moderately expensive. - Things to consider: certain cookware manufacturers claim that an anodized aluminum cooking surface is “stick resistant.” However, owners commonly report that this does not reflect their experience, and anodized aluminum pans that are not kept scrupulously clean are often quite sticky. - Common uses: Almost every pan in the kitchen is manufactured in raw aluminum. Since anodized aluminum is less reactive than raw aluminum, one need not be so concerned about minimizing opportunities for chemical interaction between the food and the pan. Nevertheless, prolonged contact with acidic or alkaline foods can still result in off flavors and colors. This design does not have any particular advantages for heating large volumes of thin liquids in stock pots, rondeaux, casseroles, etc. - Representative manufacturers: Calphalon (Commercial and Professional lines), Circulon Aluminum with an Interior Lining of Stainless Steel - All the thermal benefits of aluminum, but with a nonreactive cooking surface provided by a thin layer of stainless steel. - The aluminum layer may be raw aluminum or anodized aluminum. - Unlike aluminum alone, lined aluminum is not likely to warp. - Data: All-Clad’s interior lined cookware has an aluminum layer of 3.94 mm - Very expensive. - Common uses: Almost every pan in the kitchen is manufactured in this design. This design does not have any particular advantages for heating large volumes of thin liquids in stock pots, rondeaux, casseroles, etc. - Representative manufacturers: All-Clad (MasterChef and LTD lines) Aluminum with an Interior and Exterior Lining of Stainless Steel - This design, with an interior thermal layer completely surrounded by other metals on the inside and the outside is often called “fully clad.” - Otherwise similar to Aluminum with an Interior Lining of Stainless Steel, with the addition of an exterior layer of stainless steel. - Due to manufacturing considerations, the aluminum layer in fully clad cookware is often significantly thinner than the aluminum layer on comparable interior-lined cookware. This can negatively impact both evenness of heat and heat capacity. - May be cleaned in the dishwasher. - Things to consider: Some manufacturers claim to employ special “multi-layer” interiors that are better than pure aluminum layers. Don’t be fooled by this marketing ploy. The interiors of these pans are 99% the same as those employed in the other fully clad designs. - Data: All-Clad’s interior/exterior lined cookware has an aluminum layer of 2.03 mm. Demeyere employs an aluminum layer of 2.3 mm on woks, 3.0 mm to 3.3 mm on “conical sauteuses and simmering pots” and approximately 3.9 mm on fry pans. - Very expensive. - Common uses: Almost every pan in the kitchen is manufactured in this design. This design does not have any particular advantages for heating large volumes of thin liquids in stock pots,
rondeaux, casseroles, etc. - Representative manufacturers: All-Clad (Stainless line), Calphalon (Tri-Ply Stainless), Demeyere (“conical sauteuses,” simmering pots,” fry pans and woks). Aluminum with an Interior Lining of Stainless Steel and an Exterior Lining of Copper - Otherwise similar to Aluminum with an Interior Lining and an Exterior Lining of Stainless Steel, with a copper exterior instead of a stainless steel exterior. - Very expensive. - Things to Consider: Regardless of what manufacturers may claim, the copper exterior does not confer any of the thermal advantages associated with copper, because it is too thin to make any impact on the thermal properties of the pan. It does, however, confer many of the maintenance issues associated with copper (see below). - Representative Manufacturers: All-Clad (Cop-R-Chef line), Calphalon (Tri-Ply Copper line). Copper with an Interior Lining of Stainless Steel - Copper has the best overall thermal properties for most cooking tasks. It has excellent thermal conductivity and a high specific heat per cubic centimeter. This means that it provides extremely even heat, is very responsive and holds a lot of heat without needing to be all that thick. However, the thermal conductivity is so fast that copper pans not retain heat well once off the heat -- this is the converse of responsiveness. - Very heavy, especially in the larger sizes. - Copper tarnishes. This does not effect performance, but can be aesthetically unpleasing to some. Brushed exterior copper can be easily and effectively cleaned with Barkeeper’s Friend and a Scotch Brite pad. Mirror-finished exteriors must be cleaned with polish or (less effectively) with vinegar and salt. - Extremely expensive. - Things to consider: Although manufacturers of stainless lined copper sometimes claim that their product is better than the competition, in fact Falk Culinair developed the process by which stainless steel and copper are bonded together to make this cookware. All cookware employing this design is made from the exact same materials, regardless of price. - Data: Most of the stainless-lined copper cookware sold in America is 2.3 mm of copper bonded to .2 mm of stainless steel -- 2.5 mm of copper/stainless steel “bimetal.” Mauviel makes three lines: two “Cuprinox” lines at 2.5 mm and 2.0 mm and the “Table Service” line at 1.6 mm. This last line is meant for table presentation and not for real cooking. Make sure you know what thickness you are buying! - Common uses: Almost every pan in the kitchen is manufactured in this design. Especially useful for cooking tasks that require the ultimate in heat control (e.g., making delicate temperature-sensitive sauces) or those where it is particularly beneficial to take advantage of copper’s ability to conduct a lot of heat all the way up the sides of the cooking vessel (e.g., reductions). This design does not have any particular advantages for heating large volumes of thin liquids in stock pots, rondeaux, casseroles, etc. - Representative manufacturers: Bourgeat, Falk Culinair, Mauviel. Copper with an Interior Lining of Tin - Otherwise similar to Copper With an Interior Lining of Stainless Steel, but employing tin instead of stainless steel on the interior.
- Tin is less durable than stainless steel. After a while, the tin lining will wear out and the interior will have to be re-tinned. May not be used at high heat, as this will cause the tin lining to blister and melt. - Tin has significantly better thermal conductivity ( 0.666 W/cm K) than stainless steel. As a result, some people feel that tin-lined copper offers the ultimate in temperature control for sauce making. - Very expensive (less expensive than stainless-lined copper). - Common uses: Almost every pan in the kitchen is manufactured in this design. From a practical standpoint, probably useful to most home cooks as a dedicated pan for sauces only. I do not recommend it for home cooks. - Representative manufacturers: Mauviel Copper with an Interior and Exterior Lining of Stainless Steel - Otherwise similar to Copper with an Interior Lining of Stainless Steel, but the copper is fully clad in stainless steel. - Due to manufacturing considerations, the copper layer in fully clad cookware is often significantly thinner than the copper layer on comparable interior-lined cookware. This can negatively impact both evenness of heat and heat capacity. However, this design should confer more thermal benefits than Aluminum with an Interior and Exterior Lining of Stainless Steel. - May be cleaned in the dishwasher. - Extremely expensive. - Things to consider: Although these pans would seem to confer many of the benefits of heavy copper with none of the maintenance concerns, the cost of this cookware is so high that one is often paying substantially more for cookware with less copper than the already expensive big boys in Copper with an Interior Lining of Stainless Steel. That is a high price to pay for the privilege of throwing a pan in the dishwasher. - Data: Best estimates put the copper interior at somewhat less than 2.0 mm thickness. - Common uses: Many of the common kitchen pans are manufactured in this design. This design does not have any particular advantages for heating large volumes of thin liquids in stock pots, rondeaux, casseroles, etc. - Representative manufacturers: All-Clad (Copper Core line). Cast Iron - Cast iron has fairly low thermal conductivity and a high specific heat per cubic centimeter. This means that cast iron pans are slow to heat up/cool down, have excellent heat retaining properties and need to be quite thick to avoid hot spots. In practice, cast iron is never thick enough to provide absolutely even heat. As a result, most good cast iron pans are quite massive and the general practice is to preheat for a long time on one heat setting until the heat equalizes and the entire cooking vessel is approximately the same temperature. At this point, the pan will hold its heat and remain at more or less the same temperature throughout for long/low cooking or short/high cooking. - Cast iron is highly reactive and prolonged contact with acidic foods can create off flavors. This can be somewhat mitigated by seasoning the cast iron, which is a process whereby successive layers of cooked-on fat are built up over the porous iron surface. This limits the reactivity somewhat and provides a fairly non-stick “natural” surface. Regardless, cast iron is not recommended for cooking tasks involving acidic foods and long cooking.
- Very inexpensive. - Common uses: Skillets, chicken fryers, grill pans, Dutch ovens. - Representative manufacturers: Lodge is the only company still producing cast iron cookware, but “antique” examples by Griswold and Wagner (among others) may be found for sale. Enameled Cast Iron - Similar to cast iron in thermal properties, but with a coating of nonreactive enamel inside and out. Because it is nonreactive, enameled cast iron is perfect for cooking tasks that take advantage of cast iron’s heat retaining ability for long, low cooking. - Enamel is an insulator and has very poor thermal conductivity. As a result, these pans are not good for quick browning. Because enamel and iron have such different thermal properties, enameled cast iron must not be heated too high nor cooled down too quickly or the enamel may chip and crack. - Very heavy. - Moderately priced to moderately expensive. - Common uses: Enameled cast iron casseroles, sauce pans, fry pans. - Representative manufacturers: Chasseur, Descoware, Le Creuset, Staub. Carbon Steel - Carbon steel has a slightly higher specific heat per cubic centimeter than Iron and the thermal conductivity is even lower. At this point, there is little to be gained by going for maximum thickness, because it would take forever to heat up. As a result, carbon steel cookware is usually manufactured in a medium gauge of approximately 2.0 mm. - Similar to cast iron, the heat does even out somewhat once the carbon steel pan has been sufficiently preheated. Nevertheless, the heat will never really be even all that even, and carbon steel pans are best used for quick cooking tasks where evenness of heat is not a primary concern. - Like cast iron, carbon steel is highly reactive and needs to be seasoned. Unlike cast iron, however, carbon steel is soft and significantly less porous. As a result, carbon steel may be seasoned sufficiently in 15 minutes and old seasoning is easily removed with a scouring pad if the cook wishes to re-season the pan. - Carbon steel cookware is not cast, it is formed from sheets of carbon steel and pressed into shape. This allows manufacturers to produce a wide variety of specially designed pans for specific cooking tasks (omelet pans, crepe pans, chestnut pans, etc.). Since carbon steel is cheap, a cook can easily and affordably accumulate a number of purpose-designed pans. - Light. - Very inexpensive. - Common uses: Fry pans, sauté pans, crepe pans, omelet pans, woks. - Representative manufacturers: These pans are not particularly associated with any manufacturers, and they are all more or less the same. Black Steel/Blue Steel - This is carbon steel that has been treated by a process of annealing, which makes the surface harder and less reactive. It also imparts a distinctive black or gunmetal blue color to the carbon steel. - Because the surface is harder, black/blue steel seasons more like cast iron in terms of its durability and persistence. Because the surface is less reactive, one need not be so concerned
about minimizing opportunities for chemical interaction between the food and the pan. - Very inexpensive. - Common uses: Fry pans, sauté pans, crepe pans, omelet pans, woks. - Representative manufacturers: These pans are not particularly associated with any manufacturers, and they are all more or less the same. Enameled Carbon Steel - Thin carbon steel with a coating of enamel inside and out to render the pan nonreactive. - Extremely prone to buckle and warp, which often causes the enamel to chip. Relatively poor thermal conductivity and heat retention result in hot spots and inferior browning capabilities. - Light. - Extremely inexpensive. - Common uses: Sauce pans, steamers, coffee pots. Cookware of this design is only useful for boiling water. - Representative manufacturers: These pans are not particularly associated with any manufacturers, and they are all more or less the same. Stainless Steel - Stainless steel holds the honor of having the worst overall thermal characteristics of all the metals used for cookware. It has the highest specific heat per cubic centimeter and the lowest thermal conductivity -- not a good combination. - Needless to say, evenness of heat is out of the question and stainless steel cookware must be thin or it will never become hot. Hot spots are inevitable. - Extremely durable and strong. Warping is only a problem at the very lightest gauges. - Fairly inexpensive. - Things to consider: Don’t be fooled by “copper bottoms” that aren’t clearly a disk of some kind. This thin metal layer on the bottom quarter of the pan confers none of the thermal advantages of copper. - Common uses: Almost every pan in the kitchen is manufactured in this design. However, it is only truly useful for boiling water. - Representative manufacturers: These pans are not particularly associated with any manufacturers, and they are all more or less the same. Thus far, all the cookware designs we have discussed have been “straight gauge,” which means that they have the same thermal properties in all parts. Now we will profile two popular “hybrid” cookware designs that have different thermal properties on the bottom and the sides. Specifically, these cookware designs have materials with good thermal properties on the bottom, and materials with not-so-good thermal properties on the sides. Stainless Steel Body with an Aluminum Base - This design begins with durable, nonreactive stainless steel and adds the thermal benefits -evenness of heat, high specific heat per cubic centimeter, responsiveness -- of aluminum to the bottom of the pan. - Because the aluminum base only covers the bottom, virtually no heat is conducted from the base up into the heavy stainless steel sides of the pan. - Moderately expensive to expensive.
- Things to consider: 1) Due to the way this cookware is manufactured, the aluminum disk can never quite cover the entire base of the pan. The percentage of the base covered by the aluminum disk varies from manufacturer to manufacturer and is one indication of quality. 2) Cooks are sometimes apprehensive that foods will scorch and burn on the parts of the pan that are not covered with aluminum -- namely the sides and the portions of the base not covered by the aluminum disk -- because these are essentially plain stainless steel. This is only possibly a concern in conditions where the flame heating the pan is larger than the pan itself, and significant heat from the heat source is in direct contact with those portions of the pan. Such conditions are rare in the home kitchen, and can largely be mitigated by adjusting the flame appropriately and not using pans of this design that are too small in diameter for the stove on which they will be used. 3) Some manufacturers claim to employ special “multi-layer” bases that are better than pure aluminum bases. Don’t be fooled by this marketing ploy. The bases on these pans are 99% the same as those employed in the other aluminum disk bottom designs. - Data: Both Paderno Grant Gourmet and Sitram Profisserie employ an aluminum base that is 7 mm thick. Demeyere Apollo employs a 5 mm thick aluminum base in its disk bottom pans. - Common uses: Many of the common kitchen pans are manufactured in this design. Particularly well suited to tasks where the important area for the transfer of heat from the pan to the food is the bottom of the pan: sauté pans, tall sauce pans, rondeaux, stock pots. - Representative manufacturers: Demeyere (Apollo line for casseroles, sauté pans, saucepans and stock pots), Paderno (Grand Gourmet line), Sitram (Profisserie line). Stainless Steel Body with a Copper Base - This design begins with durable, nonreactive stainless steel and adds the thermal benefits -evenness of heat, high specific heat per cubic centimeter, responsiveness -- of copper to the bottom of the pan. - Otherwise similar to Stainless Steel Body with an Aluminum Base. - Moderately expensive to expensive. - Things to consider: Demeyere Sirocco has two interesting innovations in its implementation of the copper base design. 1) The copper base is completely enclosed in stainless steel, allowing these pans to be cleaned in the dishwasher. 2) The copper base extends the full diameter of the pan, so that the maximum possible cooking surface area is in contact with copper. However, it is not the case that Demeyere’s implementation covers 30% more of the base than the traditional implementation, as they claim. Rather, the copper disk continues to extend beyond the point where the stainless steel on the bottom of the pan begins to curve upwards to form the sides. Since the copper base does not actually contact the stainless steel beyond the point where it curves up, no heat is conducted into these parts of the pan – exactly the same as it is with the traditional implementation. This is well illustrated by this graphic from Demeyere’s web site. Again, be wary of marketing hype and take any claims of “special multi-layer conductive materials” with a big grain of salt. - Data: Demeyere Sirocco employs a 2.0 copper base for casseroles, sauté pans, saucepans and stock pots, while Sitram Catering has a 2.5 mm copper base for most pans and a 2.0 mm copper base for pans with the smallest diameters. - Representative manufacturers: Demeyere (Sirocco line for casseroles, sauté pans, saucepans and stock pots), Sitram (Catering line).
How Much Of The Various Materials Are Used Based on the foregoing, we now have basis for understanding the effects of various materials used in various amounts. We can understand that, for instance, a 4 mm thick aluminum sauté pan with an interior lining of stainless steel will provide better evenness of heat than a 2 mm thick aluminum sauté pan that is fully clad in stainless steel. Likewise, we can understand that a stainless sauté pan with a 7 mm aluminum base will hold more heat than an otherwise similar pan with a 5 mm aluminum base or a 2.5 mm copper base. We can also understand that the pan with the copper bottom will be much more responsive to changes in the heat setting on the stove while still having even heat.
So, now it is up to you to ask yourself some questions. You want a sauté pan. Fine. Do you really care whether the heat goes all the way up the sides? Probably not. OK, then. It probably doesn’t make sense to spend all the money on straight gauge cookware. Alright, we’re going with a diskbottom design. So... do we care whether the heat goes all the way to the very edge of the base? Not really. After all, we are going to be tossing the food around quite a bit as we sauté. Doesn’t make sense to spend big bucks on Demeyere Sirocco, then. The next choice is whether we want a copper base or an aluminum base. Since the kind of sautéing we do tends to be all on high heat, having lightning-quick thermal conductivity doesn’t matter all that much to us. We’ll go with aluminum then. Now that we have decided to go with an aluminum disk bottom sauté pan, all that remains is to determine the thickness of the aluminum base. This will largely be determined by economics. Since we understand that more aluminum means more heat capacity and more evenness of heat, we’ll get the sauté pan with the thickest aluminum base we can afford. Other considerations may be price, weight, aesthetics, brand loyalty, versatility/suitability for other cooking tasks -- any number of things. And, of course, these answers may not be your answers. What is important is that we will be making an informed choice. Please join me in the Q&A with your questions and comments. Post your questions here -->>Q&A Copyright 2003 Samuel Lloyd Kinsey. All Rights Reserved. Any unauthorized duplication or use is strictly prohibited.