Cooking surface: 2/5 Poor (4/5 Very Good if anodized)
Conductive layer: 4/5 Good (5/5 Excellent if over 3.5 mm thick or with thick conductive disc base)
External surface: 2/5 Poor (4/5 Very Good if anodized)
Example: Anolon Nouvelle Copper Nonstick
Health safety: 4/5 Good (5/5 Excellent if anodized)
Compared to other metals, aluminum (also known as aluminium1) is highly thermally conductive (pound for pound, aluminum delivers the highest thermal conductivity of all cookware materials), cheap, and low-density, but not particularly hard or strong. Heat treatment and other techniques can strengthen and harden aluminum, but such techniques can also make machining and forming pots and pans harder as well.
Commercially pure aluminum (1000-series aluminum, which is 99.9%+ pure) has the highest thermal conductivity of all aluminum alloys, but due to the “orange peel effect” where bonded pure aluminum can form bumps and ridges similar to orange peels due to the nature of its grain, it is not viable to use ONLY pure aluminum as the core of a cladded material (few customers would accept bumpy-looking cookware).2 Thus, typically you will see a construction like so: stainless steel, a very thin bonding layer of pure aluminum, a core of 3003 or 3004 aluminum, a very thin bonding layer of pure aluminum, and stainless steel. 3003/3004 aluminum has significantly lower thermal conductivity than pure aluminum, but you also avoid the orange peel effect.
If you are wondering why cookware manufacturers use 3003/3004 aluminum instead of some other aluminum alloys that have slightly higher thermal conductivity, it is because 3003/3004 aluminum is inexpensive, is easily formed (i.e., made into different shapes and sizes of cookware), has durability/strength good enough for kitchen cooking, and is more corrosion-resistant than many other aluminum alloys. That last factor is very important, since commercial and residential cookware is continually being banged into drawers/sinks/stovetops and being left with water, saltwater, and acids in them at all sorts of temperatures.
Cast aluminum is made like cast iron–molten aluminum injected under pressure into a mold of some sort (commercially, mold or die-casting is more likely than sand casting). The final product strongly resembles the finished product in shape and size, though some additional work remains (e.g., polishing). Higher-quality restaurant supply pots and pans are often made with cast aluminum. These are considerably more rugged than cheaper stamped or rolled pans and more warp-resistant in part because they are cast. Thicker aluminum is more warp-resistant than thinner aluminum.
Stamped or rolled aluminum is formed by taking sheets of aluminum and reforming them through pressure. The fine structure of the aluminum is stressed and if the aluminum is subjected to high temperatures and then cooled down rapidly (e.g., submerged in water right after searing a steak), there is a risk of warping. The thicker the piece of aluminum, the lower the risk of warping. Cheap pots and pans are typically made with stamped or rolled aluminum only a few millimeters thick, which might not be enough to resist warping over time.
Aluminum has a somewhat low melting point (e.g., 3003 melts below 1200F) and weakens/deforms at even lower temperatures. This is not a problem in normal usage, especially for thick aluminum, but is a potential problem if a forgetful person leaves an aluminum pan on a hot stovetop for long periods of time. In fact, one lady’s child left an aluminum-disc-base pot on the stovetop for a long time, with messy results:
All aluminum naturally has a very thin protective oxide layer that discourages further corrosion (unlike iron which can disintegrate into iron oxide, better known as rust). This oxide layer is invisible and easily scratched away or worn down by some foods such as acidic foods. However, it is possible to dip aluminum into a chemical bath to accelerate and deepen the oxidization to about 1/20,000th millimeter thickness. This product is called anodized aluminum. Anodized aluminum (usually produced in gray or black color) is much harder than stainless steel. It also conducts heat much less well, but this is not a problem due to how thin the oxide layer is; the thin layer is not an impediment to thermal transfer. Anodized aluminum is nonporous and will not suffer from the off-tastes/colors of non-anodized aluminum. It bears mentioning that aluminum oxide can still chip or flake off, though–even the thicker layers produced by anodization. It also bears mentioning that many anodized aluminum pieces of cookware have Teflon or some other weaker material that may abrade away much faster than the underlying aluminum.
Try to avoid buying bare aluminum, because it requires more care and theoretically can lead to health problems. Bare aluminum is highly reactive and instantly forms a protective oxide layer when presented with oxygen, as noted above. However, a non-anodized aluminum surface is fragile and you can easily scratch it away. There may also be gaps in protection that allow metallic/off-tastes and off-colors, especially with foods that react with aluminum oxide to strip away that protective layer, such as acidic or salty foods like tomatoes or sauerkraut. Some people believe that consuming too much aluminum can lead to Alzheimer’s Disease, but that is based on discredited studies decades ago. Very small quantities of aluminum come off cookware in the first place, not large enough to be harmful for adults.3 (As an aside, some claim that the World Health Organization estimates that the average adult can intake up to 50 mg of aluminum per day without problems, but that may be an outdated recommendation, as I have not been able to find any such statement in their more recent documents.)4 Nevertheless, it’s not a good idea to willingly ingest aluminum if there are other options available–and there are, such as anodized aluminum.
For those who deem aluminum unsafe anyway, please note that many restaurants use cheap bare aluminum cookware due to cost and also because the restaurant owners don’t want employees destroying or stealing expensive cookware. Thus if you eat at restaurants, you are likely getting aluminum exposure that way anyway. Indeed, you even will find aluminum in drinking water.5
If possible, buy rivetless aluminum cookware. This is because aluminum cookware typically comes with aluminum rivets, and aluminum rivets can weaken with time. Aluminum cookware can come with stainless rivets in theory, but the harder rivet will just chew a bigger and bigger hole in the aluminum with use, to the point where the rivet loosens and becomes useless and causes leaks. (Stainless cookware can use stainless rivets just fine, since stainless vs stainless is an even match.) The Vollrath Wear-Ever Ever-Smooth series is comprised of all-aluminum pans with flush rivets. Some models come coated with PTFE/Teflon (nonstick), if you are worried about cooking on bare aluminum. If you don’t care about rivets or cooking on bare aluminum, there are 100% all-aluminum, riveted cookware lines that may be cheaper, such as Vollrath Arkadia.
Aluminum is relatively soft and will be dinged up and scratched before you know it, by the burner grates or metal utensils. Even anodized aluminum will chip/flake off if you strike it against other hard surfaces enough times. Thin aluminum will warp over time, which can be a problem if you have a flat cooktop. To avoid this, try to buy relatively thick (3mm+) aluminum with either anodization or a stainless steel disc on the bottom or both. Also avoid large temperature shocks like pouring cold water over a hot aluminum pan, as that is a great way to warp your pan.
Aluminum is not compatible with the vast majority of induction cooktops. There are a few expensive, exotic induction cooktops that will (inefficiently) work with aluminum and copper.
It is not necessary to season bare aluminum or anodized aluminum.
Try to avoid using putting your aluminum cookware through dishwashers with harsh detergent. Even anodized aluminum may have a few small spots of weakness where the anodized layer chipped off, and harsh detergents may eat away at the exposed aluminum. This is particularly a problem for cladded designs where the aluminum layer is between two thin (~0.5 mm thick) stainless steel layers. If the aluminum gets eaten away, you are left with two very thin, stainless steel edges that can cut fingers and sponges. If you absolutely must wash aluminum with a dishwasher, try using detergents that explicitly state that they are safe for use with aluminum.
Aluminum is often coated with PTFE such as Teflon, which is nonstick. This is good for things like making eggs, but less good for high-temperature searing due to PTFE high-temperature safety concerns, and also because food does not develop fond as well on nonstick. In addition, most nonstick aluminum is dark, making it harder to see fond. It is not necessary to “season” aluminum cookware.
- As a side note, both aluminum and aluminium are correct spellings. The International Union of Pure and Applied Chemistry (IUPAC) accepts both. Both derive from “alum,” the salt that contains aluminum, which in turn was derived from French, which was in turn derived from the Latin name for alum, “alumen.” British chemist Sir Humphry Davy named the anticipated-but-yet-to-be-discovered element several times, including “alumium,” “aluminum,” and “aluminium,” changing his mind several times between 1807-1812 before settling on “aluminium” to make it sound consistent with other elements he had previously named, like sodium. However, other metals like platinum predated aluminum and did not have the “i” before the “um,” and “um” is arguably more grammatically correct since alumina is the oxide, not “aluminia.” ↩
- “Aluminum’s lightweight and easy cold working make it a suitable material for the manufacture of high quality cookware. The aluminum core of such a product is usually an ‘Alclad’ type product Which is a prebonded strip of aluminum With a very thin skin of a higher purity aluminum (EC grade, or 1100, 1130, 1230, 1175, 7072, 1050, 1145, 1060 and like 1000 series alloys, etc.) on the exterior and an aluminum alloy core. The pure aluminum is needed in proximity to the stainless steel to achieve a suitable bond and the aluminum alloy core is present for its deep draw characteristic due to its higher strength. The aluminum alloy layer also prevents the ‘orange peel’ phenomenon which would cause a rough texture on the exterior surface of the drawn product. Because of the nature of its grain, this can occur when a core of solid pure aluminum is used.”–All-Clad patent application, US6267830 ↩
- Early studies thought there was a link between Alzheimers and aluminum intake, but those have since been discredited. Aluminum is extremely abundant in our natural environment. The average daily intake of aluminum for Americans is about 10 to 50 mg, and cooking with bare aluminum would contribute less than 5 mg extra. People with elevated aluminum intakes on the order of 1000 mg per day have no increased incidence of Alzheimer’s Disease. Dr. Charles DeCarli, director of the Alzheimer’s Disease Center at the University of Kansas Medical Center states that, in his opinion, “the supposed relationship between aluminum and Alzheimer’s Disease is a simple case of neuromythology.” Great Misconceptions: The Science Behind the Myths by Karl Kruszelnicki (Andrews McMeel Publishing, August 1, 2006), ISBN-13 978-0740753640 at 132. As for dying from aluminum poisoning, that is indeed possible, like it is possible to die from drinking too much water too fast, but it’s unlikely that the few milligrams of aluminum from bare aluminum cookware would make a difference (see above). Still, try to avoid intake of aluminum whenever possible; don’t go out of your way looking for trouble by doing something like consuming lots of aluminum-heavy antacids while dousing yourself with aluminum-containing deodorant every day and cooking with bare aluminum three times a day. Ingesting or breathing large amounts of aluminum can be harmful. For instance, aluminum factory workers should breathe via filters to limit aluminum particle intake. http://www.atsdr.cdc.gov/phs/phs.asp?id=1076&tid=34 ↩
- World Health Organization Background document for development of WHO Guidelines for Drinking-water Quality accessed at http://www.who.int/water_sanitation_health/dwq/wsh0304_53/en/index2.html ↩
- Id. “Aluminium metal is used as a structural material in the construction, automotive, and aircraft industries, in the production of metal alloys, in the electric industry, in cooking utensils, and in food packaging. Aluminium compounds are used as antacids, antiperspirants, and food additives (ATSDR, 1992). Aluminium salts are also widely used in water treatment as coagulants to reduce organic matter, colour, turbidity, and microorganism levels. The process usually consists of addition of an aluminium salt (often sulfate) at optimum pH and dosage, followed by flocculation, sedimentation, and filtration (Health Canada, 1993).” ↩