Hard Anodized Aluminum vs Stainless Steel?
- dcole Mar 10, 2009 05:47 PM
Is there much difference in conductivity between the two exteriors if they both have aluminum interiors and stainless steel cooking surfaces?
I'm a little confused by your terminology, since interior of a pan is the cooking surface, and thermal conductivity is a property of the metal, not the pan. I'm thinking maybe you just want to know which pan will heat up faster, which is thermal conductance. Thermal conductance depends on both the conductivity and the thickness the metal (or each layer for composite pans), so a thin steel pan might actually heat up faster than a thick aluminum one, even though aluminum has better conductivity.
Anodization will have little or no effect on conductivity, so a solid aluminum pan will have greater conductance (i.e. the cooking surface will heat up faster) than a layered aluminum/stainless pan if they have the same total thickness.
There are so many factors to consider when selecting a pan, but if you want one that heats up quickly and easily, I suggest anodized aluminum. The anodized surface is not really non-stick, but it is a bit easier to clean than bare aluminum. Nothing wrong with a good stainless pan with an aluminum or copper bottom, though.
And they said I'd never use anything I learned in thermodynamics.
If a particular pan comes in three possible materials: Stainless Steel, Aluminum, and Hard Anodized. The suggested retail prices are equal for the Stainless Steel and Hard Anodized and the Aluminum is about 33% less. Supposing the Stainless Steel doesn't have an aluminum or copper core, would the best choice be the aluminum because it's cheeper than the anodized and that anodization doesn't actually add anything? If, however, the stainless steel does have an aluminum or copper core would it be equal (in terms of function) to the aluminum (regular or anodized)? Supposing a non-stick coating on the actual cooking surface of all three options, would the choice between anodized, stainless (with a core), and aluminum be purely cosmetic (and/or price)?
I chime in with Zeldog. "Anodized" usuallly means
a pan composed entirely of aluminum.
anodized on the inside and outside.
An all-aluminum pan should have a bit
better conductivity than one with stainless
steel and aluminum .layers. In actual use, however,
you won't find much difference. With any material,
you'll still need a little personal experience
for optimal results.
Can't answer your question directly, but I want to share my experience with HA, stainless, and all-aluminum pans (not HA). I've been using Calphalon HA since the early 90's and never really liked the skillets/saute pans for cooking eggs, breaded or floured meats, poultry, fish, and the like because everything sticks. Experienced the same thing with stainless. I haven't ever had the good fortune to have a gas stove, only electric coils or, currently, ceramic top so the fuel source may have something to do with it.
But out of desperation and loathing for my calphalon skillets and for non-stick I recently bought an aluminum skillet at a restaurant supply store - the pan is cast aluminum with a polished interior that makes it look like stainless, but it's not stainless. And let me tell you this pan cooks like nonstick. Eggs, scrambled or fried, don't stick, at least no more than they do in a nonstick pan, and finally when sauteeing I can obtain the lovely fond that I couldn't get from non stick and that that ended up not brown but blackened and inedible in stainless and HA.
As an aside I've had a similar experience and eureka moment when I purchased aluminum half-sheet and quarter-sheet pans. These are so great, nothing sticks, easy to clean, and so far superior to any other sheet pan, cookie sheet, or jelly roll pan that I've ever purchased. I really don't understand why such cookware isn't easier to find.
Anyway hope this helps.
I've built restaurant for many years and have in recent years developed a fondness for learning to cook more. I was interested in the aluminum skillet method but cautious about where to buy, as most aluminum has lead in it. What was the brand of aluminum skillets you purchased?
I had considered the new Calphalon series, but for some reason I couldn't figure out the distinction between the slide and sear, and which I would use when. So I bought neither. But since I wrote about my experience with my 30+ year old hard-anodized Calphalon, I have to revise what I wrote last January. I no longer loathe my calphalon pans. I have both saute pans and skillets, and over time both types of pans have developed a good patina, especially the skillet I use all the time for pan roasting nuts. I love my calphalon cookware, and still love the other aluminum pans as well. The stainless, not so much, but it is good for browning ground beef and for making poached eggs. That's all I use it for, otherwise I turn to either type of my aluminum skillets.
I have a set of old Calphalon Anodized cookware (before they added nonstick stuff on the inside). Yes, the solid aluminum transfers heat more quickly and evenly. These pans are thick, not chintzy thin aluminum. The anodized surface browns food better. It releases the food when it is browned, if you mess with it before it is ready, it sticks like crazy. Not the pans for impatient cooks who need to mess with their food.
It's horses for courses. As Zeldog says, it is a mixture of things. Woks for instance need to be thin so they can be heated very quickly. Cast iron pots (I use le Creuset) take ages to heat up, but then you have to keep them down [i]really[/i] low to prevent burning. Good stainless steel never gets damaged. I use them for the majority of my cooking. They are easy to clean with wire scrubbers. However, if I want to fry and egg or scramble one then non-stick every time.
My best pans are multi layered, with aluminium, copper and stainless. The copper provides better conductance than aluminium (sic) - and therefore a more uniform pan temperature. But they are 35 years old now.
And sometimes you don't want a uniform pan temperature. (eg Woks)
That fact that wok cooking does not require uniform temperature is important. It takes advantage of the fact that the center bottom is quite hot, and rim much cooler. Hence relatively thin carbon steel works well.
When traditional cooking wants uniform temperatures, it often uses some form of terracotta or ceramic. The Chinese have their sand pots, the Spanish their casuelas. I've even seen wok shaped Spanish terracotta.
I use to cook a lot. As an enginerd, think this:
Stainless heat conductivity = 16 W/mK
Aluminum = 250
Copper = 400
>>>So Aluminum thermal conductivity is 16X that of Stainless Steel<<<
However, we do not have aluminum in real life, unless you polish it hourly to keep it shiny. We get a very thin film of aluminum oxide (="anodize"), only a few thousandths of a inch thick covering the aluminum. Alumiinum ocxide is rust, but this kind of rust is so hard that oxygen cannot further penetrate the base layer of aluminum to keep it rusting.
Aluminum oxide thermal conductivity = 30 W/mk
This applies to per thickness of material, so a thin aluminum oxide or stainless steel coating affects less than thick. It's a straight ratio, twice as thick = twice as much thermal resistance.
... or thereabouts...
Also, chew on this: each time you layer materials, you form a disjunction for heat transfer. The amount depends upon the pressure between the surfaces and surface irregularities. That's partially why sitting on a cold stone floor in you undies is way more tolerable than bare naked (however might depend on the company you keep, even enginerds need stress releases).
What I'm saying is that "clad" is ka-ka. Stainless is ka-ka. Bare aluminum is toxic.
JannieCooks polished aluminum skillet might be nickel plated. Anodizing is not "on top" of the aluminum, it's an oxide conversion that is "soaked" in top few .001"s, so it'd be real hard to make shiny.
As a cook, I like cast iron. Just got to get the pan hot FIRST. TC = 55 W/mK. Can scrape it, cut on it, etc.. I want a new Wagner, I'm down to a replacement All-clad now, which is coated with a "teflon" non-stick which comes in the form of a ceramic. Which came off my first All-clad, even tho I use wood & rubber utensils.
Back to work now. I'm making some press to cook electronic parts today and just surfed across this thread.
Stainless steel is protected by the same sort of oxide layer as aluminum. For most types of SS, the oxide layer is made from the chromium in the alloy, though there are very high temperature steels that depend more on aluminum. These very high temperatures of typical of jet engines, not home stoves.
For even heating, the spread of heat sideways through the pan (from parts in contact with the heating element to parts further away) is more important, than the short distance spread through the thickness of the pan. If you want quick transfer of heat from the burner to the food, it would hard to beat a disposable aluminum pie plate. Sandwiching a layer of aluminum (or copper) between two layers of stainless steel is not going to improve heat transfer straight through the bottom of the pan. Its purpose is to spread the heat out, reducing the formation of hot spots. However a layered pan should have better conductivity (straight through) than a pure SS pan of the SAME thickness (provided the bonding between layers is done right).
reburns, I'm not sure I get what you're saying, but that's okay, it's not my intention to dispute your science. Just wanted to make it clear that my polished aluminum pan is not hard anodized, it appears to be a layer of polished aluminum (it looks like stainless steel) sandiwched with a different outside layer of aluminum. Unless it is common for commercially sold aluminum pans labeled as made of aluminum to include nickel, there is no nickel in them. So are the mfgrs mislabeling their goods?
I agree that Misah Paulj is correct in the thinking that the goal is to distribute the heat versus the pie-pan analogy. That notion changes my thinking - maybe that's why the cast iron is so nice. And correct that the chromium forms an protective oxide layer in Stainless but I recon it doesn't make much of any difference our cooking qualities..
Paulj, tell us why stainless sticks so bad!
Does copper give hot spots? My only copper pan is el-cheapo thin.
Janniecooks, I was just surmising that there is a coating on top of your aluminum pan, because aluminum doesn't stay shiney. Not saying that it's added into the aluminum alloy, but plated on top. When you say shiny, I'm visualizing that you can almost see you face in it.
I can make some guesses about sticking/nonstick, but I don't know for sure. There appear to be two types of surfaces that have low stick qualities, polymers and glass.
Teflon is a synthetic polymer, the seasoning on cast iron and steel a natural one. I think a polymer is a long-chain organic chemical, but I don't know why it has non-stick qualities. Cast iron (and carbon steel) may develop a seasoning because the polymer can lock into the pores. The chromium oxide layer on SS may not be porous enough. Plain aluminum does not develop a seasoning either (judging from experience with a couple of restaurant quality pans).
The other low stick surface is glass like. Examples are glazed terracotta, and enameled steel and cast iron. Chinese sand pots, and Spanish cazuellas are surprisingly nonstick. I'm inclined to say these are low-stick because the surface is 'smooth', but that might not be accurate. Viewed with a microscope, enamel might not be any smoother than stainless steel.
Hard anodized aluminum appears to be moderately low stick; not as good as the polymers and the glass, but better than stainless steel or bare aluminum. I suspect that is because anodizing produces a porous glass-like surface. I have one hard anodized cooking surface - an aluminum dutch oven. It does not develop a seasoning, so the pores may be smaller than on cast iron.
Some manufacturers apparently try to produce durable nonstick surfaces by creating a rough but hard surface ('diamonds'), and filling the gaps, or pits, with a polymer. The bumps help anchor the polymer, and provide a hard wearing surface.
Did you mean hard anodized is porous or non-porous? I have seen it described both ways and wondered if it depends on the actual process used for anodization. I have some Calphalon One and the claim seems to be that a release polymer (sounds a lot like PTFE) is in the pores.
Food sticking is a strange phenomenon, and HA is an unusual material. Tonight I cooked one of my favourite comfort food combos, Nigella's Mustard Pork Chops with fetuccini, and Baked Tomatos Provencal. When I slammed the pork down in the hot oiled anodized aluminum pan it stuck like contact cement: hard and fast. I thought it was down for the count. As it cooked, the words of a long ago cooking instructor, Chef Ian, repeated through my mind. "It will release." And sure enough, at the appointed doneness, like magic, it released from the pan. And boy did it have a nice seared brown surface crust. Cook the 2nd side, deglaze with a little apple cider, add cream for a sauce, toss in the fetuccini and we had another happy meal!
According the tables that I just looked at, heat capacity for aluminum is about twice that of iron - per mass. But converted to heat capacity per volume, that of iron is 50% higher. Copper is about the same as iron (per volume).
The role of heat capacity of the pan in cooking is tricky. In some cases high heat capacity is bad (if you want quick response to the stove flame), in others good (if you want to keep food warm off the stove).
I'm an applied physicisists, and think I can shed a little light on this subject. Several people have touched on the different material properties, but I'll try to put them all together.
HA - ALL aluminum has an oxide layer since Aluminum oxidizes more rapidly than any other metal (except for maybe Yttrium or Niobium). What makes the HA unique from regular aluminum is the anodization process, which uses an electrical current/voltage gradient to control the oxidation process. The result should be (without knowing each manufacturer's process it's hard to tell) a very uniform coat of aluminum oxide on the cook surface. If you start out with a porous, rough surface finish, this could easily be preserved through the anodization process (especially if it's short), and it's my understanding that pores = sticking when no release agent is present. The shiny aluminum pots don't have a coating, they were polished before anodization, and probably after as well. The shiny surface finish has fewer rough spots, so it's less porous and won't stick as much. Nickel plating shouldn't happen in cookware, it's not necessary.
Regarding the thermal properties, aluminum is one of the top five metallic conductors (electricity and heat, they're both mediated through the same process at reasonable temperatures!), which means it can result in a very even cook surface. However, the thickness is incredibly important in determining how even the temperature can become. If you have a strong flame under a thin pot, you will get hotspots because the rate of heat into the cookware is greater than the rate at which the cookware can dissipate heat across the surface. Thicker cookware allows more cross sectional area for heat dissipation, resulting in a much more even temperature.
The last part of the equation is the heat capacity of the pot. It's much easier to think in terms of thermal mass, or the product of the heat capacity of the material and the mass. The larger the thermal mass, the more energy stored in the pot at a given temperature. This means you have to loose more energy to lower the temperature of the pot. This is critical for searing, especially in an HA pan. Since aluminum is such a good thermal conductor, when you place a cold (relative to the pan!) object in contact with the surface, heat will immediately move to the cold spot. Invariably, your pan will cool, and if you don't have enough heat (energy) stored in the pan, your pan will cool too much and you won't get that nice sear. Thermal conductivity does factor into this as well, since it determines how quickly heat will reach the cold spot. This is why cast iron is used in blackening, the thermal mass is HUGE, and the thermal conductivity isn't horrific. Based on some rough calculations, an HA pan that's twice as thick as a SS pan would have about the same thermal mass. In that case, the HA pan would be just a little lighter than the SS.
SS - A stainless steel pot of the same dimensions as an aluminum pot will have better heat capacity properties than the aluminum pot, but won't be as even. This is where copper bottoms (not cladding!) come in. Copper is a better thermal conductor than aluminum, and it has better thermal mass properties. So, if you have a nice slab of copper under your SS pot, the heat will be evenly spread across the copper, which is nearer to the burner, and this heat will diffuse into the SS, creating a very even heating surface with a nice thermal mass. Could you get this with just a thicker SS pan? Maybe, but you would invariably have more hotspots than with the copper bottomed pot. Just as a note, copper bottom is not equal to copper clad. A few thousandth's of an inch of copper at the bottom of a pot just won't have the same effect as a solid slab of copper. The one problem with the multilayer materials is the boundary between the two materials results in non-uniform properties. Since you're cooking in the stainless steel, you're still limited by the thermal conductivity of the SS, and when your ingredients hit the pan, you'll get some hotspots/cool spots, but the copper will definitely help. Ideally, we'd all cook in thick copper cookware, the best combination of thermal mass and conductivity that I know of, but it's just too expensive for most of us.
Cast Iron - The huge thermal mass is perfect for searing (I learned to cook in cajun country, so blacken away!) and for simmering stews with very even heat. The thermal conductivity of the iron means you will get hot spots if you're pumping a lot of heat into the pot. That's why cooking over a campfire, a bed of coals, or a gas grill is better with the cast iron than a range, which almost always has a circular hot spot. At low temperatures, the thermal conductivity of the pot does a much better job keeping up with the heat that's coming in, and you get a very even, very steady cooking temperature.
HA sounds great, as long as it's heavy and made through a good annodization process, I'd look for a shiny surface.
SS is fine for most people, and the copper bottom makes it much better. Again, you need a thick skillet!
Cast Iron may not be practical for everyday cooking, but for searing, I don't know of anything that beats it. I cook my eggs in here as well, and the seasoning keeps them from sticking. Just don't cook acidic foods in cast iron, they'll ruin your seasoning and lead to rust.
Always remember, if you want to prevent sticking, start with a hot pot! You can prevent sticking when you start with a clean, hot surface. When an ingredient hits the pan, the water inside will turn to steam and some of htis steam has to come out. This will disrupt sticking to some degree, no matter what you're cooking in.
That's it, let me know if you disagree or if that helps anyone out.
All-Clad LTD2 is five-ply, the central layer being SS, surrounded by aluminum. The idea is to slow the heat transfer directly through the pan to give the outer aluminum layers more time to conduct the heat to the sides. This is supposed to produce more uniform heating compared to original LTD and MC(2) lines. I don't know how well this works.