Stainless steel is also known as “stainless.” Since a lot of cookware is manufactured in French-speaking countries, you may see the terms “acier inoxydable” or “inoxydable” or “inox” which mean all mean “stainless steel.”
So what is stainless steel?
The short story: stainless steel is a corrosion-resistant type of steel. It’s much harder and has a much higher melting point than aluminum and copper, making it the most durable of all common cookware materials. (Porcelain/ceramic/glass and anodized aluminum are harder than stainless steel, but they are also brittle, making them more likely to break if dropped or bashed against the side of a sink or other hard surface.)
However, stainless steel is not 100% corrosion-resistant. Even the most corrosion resistant grades of stainless steel will eventually pit/stain/rust if exposed to salt water or acid for long enough periods of time. Thus you should never store acidic foods (e.g. tomato sauce) in stainless steel pots overnight. Also do not use undissolved salt as that is highly corrosive, and even the best grades of stainless steel can’t resist that abuse indefinitely. For instance, when making pasta, bring water to a rolling boil first before adding salt. The agitated water will prevent salt from sinking to the bottom of the pot before it has a chance to dissolve. Stainless steel cookware can last a lifetime–with proper care.
If you’re shopping for stainless steel kitchenware, the hierarchy goes something like this:
- BEST stainless steel (most corrosion-resistant): 316 Stainless (also known as 18/10: this is steel that is 18 percent chromium, 10 percent nickel by mass).
- 304 Stainless (also known as 18/8 stainless). A lot of stainless marketed as 18/10 is actually 18/8.3. Still very corrosion-resistant.
- Chantal Induction 21 Steel is a rebranded steel known as JYH21CT, which was invented in Asia as a cheaper alternative to 304 stainless. It has similar corrosion resistance but is cheaper to make because of the lack of nickel (nickel improves hardness and corrosion resistance in stainless steel but costs ~200 times more than iron). Chantal 21 adds the following elements to iron: 21% chromium, 0.3% Titanium, 0.008% Carbon, 0.01% Nitrogen, and 0.43% Copper. Chantal contrasts this to their 18/8 stainless which adds 18.2% Chromium, 8.2% Nickel, 0.06% Carbon, and 0.04% Nitrogen. Therefore the main difference is that Chantal 21/0 has slightly more chromium (21% vs. 18.2%) and no nickel (0% vs. 8.2%). Chantal claims that its 21/0 stainless conducts heat 30% faster than 18/8 stainless, but who cares? 18/8 is a poor heat conductor, so 30% faster than terrible is still terrible. The bottom line: unless you are one of the few people with nickel allergies out there, you probably won’t get much if any benefit from going to Chantal 21/0 compared to the 18/8 and 18/10 that most manufacturers use.
- SAE 200 series stainless (18/4 Stainless). Still very corrosion-resistant but try not to do all-day-long salty/acidic braises in this grade of steel as it is not as corrosion-resistant as 18/8 or 18/10.
- 18/0 Stainless. Corrosion-resistant enough to survive the dishwasher without rusting. It’s also magnetic, so most induction-compatible cookware uses 18/0 (SAE 400 series) steel on the bottom.
- WORST stainless steel (least corrosion-resistant): You may occasionally find other grades of stainless like 14/1 or 14/4 stainless, often produced in India. Oftentimes the manufacturer is too embarrassed about the quality of the stainless steel to disclose the grade of stainless steel. Personally, I try to avoid Indian stainless due to lower quality control and because so much of it is poor-quality stainless.
Many cookware manufacturers do the bare minimum to meet legal standards for marketing. Thus if they say “stainless” with no elaboration, it probably means a cheaper type of stainless, because if they were using more nickel, they would brag about it in their marketing materials. If a cookware manufacturer says “magnetic” stainless steel with no other explanation, it’s likely something like SAE/AISI 430 grade stainless steel (18% chromium, 0% nickel).
Finally, stainless steel is considered a healthy surface on which to cook; it does not produce off-flavors when confronted with acidic food, and only insignificant amounts of stainless steel alloys leach into food (though people with nickel allergies may want to avoid any stainless steel that is not labeled “nickel-free”1). Stainless steel is also affordable, easily cleaned, has a high melting point, and does not emit health-threatening fumes like overheated nonstick PTFE such as Teflon can.
Regular steel is a mixture (“alloy”) of elements: mostly iron, with small amounts or traces of aluminum, carbon, manganese, oxygen, nitrogen, phosphorus, silicon, and sulfur. Regular steel is not corrosion-resistant; iron in the steel combines with oxygen from air or water and creates iron oxide, better known as rust. Rust is bulkier than the rest of the steel and can flake off (e.g., due to gravity), exposing more steel to oxygen. The process repeats until all of the steel turns into rust.
To make steel “stainless,” chromium is added to the iron. “Stainless” steel is defined as steel having at least 10.5% chromium by mass. Chromium oxidizes like iron, but unlike iron oxide (rust), chromium oxide is a smaller molecule that binds tightly to the rest of the steel, forming an invisibly thin protective barrier against further oxidization. The more chromium content in steel, the greater corrosion resistance. If the chromium oxide layer is disturbed, such by scratching, a new layer will form if there is enough oxygen present. Thus stainless steel is said to be self-healing.
For purposes of cookware, you may see grades like “18/10” or “18/8” or “18/0” advertised. In theory, the first number is the percentage by mass of chromium; the second number is the percentage by mass of nickel (which hardens stainless steel and helps with corrosion resistance and also makes stainless steel shinier). 18/8 stainless therefore means steel with 18% chromium and 8% nickel by mass.
18/10 doesn’t necessarily mean 18/10% chromium/nickel. In the U.S., there is no such thing as 18/8 or 18/10 anymore, it’s all just SAE 304 stainless which specifies 18-20% chromium and 8-10.5% nickel, which a typical composition of 18% chromium and 8.3% nickel. So as long as you use 304 stainless with at least 8.3% nickel, you can call the result 18/10. Cookware manufacturers have taken advantage of this legal leeway, meaning there might not be any significant difference between cookware marketed as 18/10 vs. 18/8. (Why might manufacturers skimp on nickel? Because it’s 240 times more expensive than iron, as of early 2015.)
If we want to be more accurate than cookware manufacturers’ marketing claims, we should use specifications according to SAE International (which effectively took over for the American Iron and Steel Institute, or AISI; if you see steel grades defined by AISI or SAE, they mean the same thing). When a modern-day cookware manufacturer asks a steel producer for steel, they ask for “SAE 304 steel,” not “18/8 steel.”
SAE/AISI 304 stainless means steel with 18-20% chromium and 8-10.5% nickel. If a cookware manufacturer claims 18/8 or 18/10, they probably mean it’s SAE/AISI Type 304. For instance, All-Clad Copper Core markets its cookware as using 18/10 stainless steel but in fact uses SAE 304 stainless steel as a cooking surface, presumably at 8.3% or higher nickel. (See, for instance, US Patent 6267830, in which All-Clad writes, “The stainless steel layers preferably are made from type 304 grade.” This means All-Clad has leeway to use anything ranging from 8.3% nickel to 10.5% nickel.) Cookware manufactures generally use the cheapest grade that still meets their advertising claims, so I’d be willing to bet that All-Clad uses something closer to the low end of that range (18/8) than the high end (20/10.5). 304 stainless has thermal conductivity 16.2 W/m-K, and a melting point 2550F (1400C).
SAE/AISI 316 stainless means steel with 16-18% chromium and 10-14% nickel, plus molybdenum of 2-3% which gives extra corrosion protection against salt. It is comparable to the outdated 18/10 stainless classification. Some commercial food processing equipment is made with 316 stainless, but rarely used in household kitchenware because it’s assumed that home cooks don’t abuse their kitchenware enough to warrant the extra expense. 316 stainless has thermal conductivity of 16.3 W/m-K and a melting point of 2500F (1370C).
SAE/AISI 430 stainless (16-18% chromium, 0.75% nickel) is magnetic and is thus suitable for use as the bottom-most material in cookware to make the cookware induction-compatible. (See, e.g., U.S. patent 20060283844 discussing 304 and 430 interior/exterior stainless steel for a Meyer Corp. induction-compatible pot.) Stainless steel with significant amounts of nickel added is usually not magnetic, so you can think of 430 as 18/0 stainless. Since there is no expensive nickel in magnetic stainless steel, it’s cheaper to make than the usual 18/8 or 18/10 stainless steel found on the interior (cooking) surface of cookware. Thermal conductivity is 26.1 W/m-K; melting point is 2600F (1425C).
Occasionally you may see “type 305” stainless advertised, which is 17-19% chromium, 10.5-13% nickel. This is theoretically more corrosion-resistant than 304 depending on exactly how much chromium and nickel are in there.
Also, cookware made for non-US markets may use other designations of steel that may differ somewhat from SAE/AISI grades. At least one company, Demeyere, uses an electrochemical process to remove iron atoms and “impurities” from stainless steel cookware surfaces, thus increasing the percentage of chromium and nickel on the surface. This makes the steel harder and even more corrosion-resistant.
Demeyere once produced a ControlInduc line of pans, which use a special kind of steel that becomes nonmagnetic above 250 degrees C. This means that it’s impossible to heat a ControlInduc pan above 250C on an induction stove. The exact alloy used is probably a high-nickel alloy (35%+ nickel). (Usually adding nickel to iron results in something that’s not ferromagnetic at cooking temperatures, but at high enough nickel concentrations the resulting alloy becomes ferromagnetic again–up to a certain temperature, the so-called Curie point, in this case 250C.) Such high-nickel alloys are much more expensive than stainless steel, and sometimes less rust/corrosion-resistant as well. I would not buy any ControlInduc products because of the price premium and possibly lower rust/corrosion resistance, and the fact that cues like smoking oil or burning food will tell you when you’re overheating a pan, anyway.
Sometimes cookware is made with titanium as a hardening agent instead of or in addition to nickel, but this seems to be more for marketing purposes rather than adding any appreciable benefit. Still others market nickel-free stainless steel cooking surfaces, made out of SAE 430 stainless steel (melts at about 1450F) or sometimes more exotic blends like 21/0 stainless.
Also, “surgical grade” does not necessarily mean anything, because it is not well-defined for cookware. For instance, this steamer basket is advertised as both 304 surgical grade, but I would prefer that my surgeon used a higher grade like 316.
HOW CAN I TELL THE COMPOSITION OF STAINLESS STEEL?
Beware of companies that lie about what grade of steel they use. There’s a cheap and easy way to tell 18/8 or 18/10 (SAE 304 or SAE 316) stainless steel apart from lower grades: use an ordinary kitchen magnet. SAE 304 and 316 use modest amounts of nickel (8 to 10% by mass), which makes 304/316 stainless steel nearly non-ferromagnetic at room temperature. (High-nickel alloys can be ferromagnetic, but nickel costs about 240 times more than iron. Virtually nobody uses high-nickel alloys for cookware for that and other reasons.)
Without getting to deep into the physics involved, 304 and 316 stainless is austenitic (face centered cubic crystal structure) and is not ferromagnetic unless work hardened (mechanically deformed). Even after work hardening, 304 and 316 is only mildly magnetic–not magnetic enough to work on induction cookers, for instance. Translation: if a magnet does not strongly stick to stainless steel, then the stainless steel is likely to be genuine 18/8 or 18/10 stainless. If the magnet strongly sticks, then the stainless steel is a cheaper grade with less nickel.
What do I mean by “strongly” sticks? I mean the magnet strongly attaches with a nice “clack” sound. To measure this more quantitatively, I took a Oxo magnetic mini clip and clipped it onto zip-loc bags full of nickels. (Yes I’m using nickels to measure nickel content of stainless steel. Haha.) I hung the clip on random cookware I owned and discovered that all of my genuine 18/8 and 18/10 stainless steel cookware would not support 38.7 grams of weight or more (including the weight of the zip-loc bag and the magnetic clip).2 In contrast, magnetic stainless steel (18/0) supported over 100 grams of weight.
I wrote down results on the table below. “Pass” means that all testable portions of a product (e.g., handles and lids) supported no more than 38.7 grams (1.37 ounces) of weight. “Fail” meant that at least some portion of a product supported more than 38.7 grams of weight. Non-testable portions of products include tri-ply material, where the exterior is supposed to be magnetic and lies only a few millimeters away from the cooking surface. It’s just too hard to determine the magnetism of the cooking surface layer of steel with that magnetic layer interfering.
CenturyLife.Org Cookware Magnetism and Radiation Test Results
|All-Clad||Copper Core||Lid Failed||No|
|All-Clad||Master Chef 2 aka MC2||Lid Failed||No|
|All-Clad||Copper Clad aka C2||Lid Failed||No|
|All-Clad||Emeril Pro-Clad||Lid Failed||No|
|Cooks Standard||Multi-Ply Clad Stainless||Pass||No|
|Cuisinart||Cuisinart MultiClad Pro||Pass||No|
|Demeyere||Resto Egg Poacher||Pass||No|
|Paderno World Cuisine||Triple-Ply Stainless||Pass||No|
|Paderno World Cuisine||Grand Gourmet Series 1100||Pass (lid untested)||No|
|Sitram||Profiserie (PPRO1)||Lid Failed||No|
|Update International||SuperSteel||Fail: cooking surface (lid untested)||No|
|Vollrath||Optio Stainless||Fail: cooking surface (lid untested)||No|
|Zwilling J.A. Henckels||Sensation aka Demeyere 5-Plus or Industry5||Pass||No|
As you can see, I caught some brands red-handed. All-Clad and Sitram Profiserie are well-regarded brands, and they both advertise the use of 18/10 stainless steel. However, both brands are not using 18/8 or 18/10 stainless in all of their lids; it appears that in many cases they are using something cheaper and less corrosion-resistant like 18/0 stainless. (I did find that some All-Clad lids were not magnetic, but why not all?) Considering how much moisture might hit the lids while cooking or washing, this is something of an annoyance. These allegedly premium brands should ashamed of cutting corners like this. Sitram’s Profiserie lids are particularly disgraceful considering how thin they are and how tiny the handle is (the handles get hot in a hurry).
As a rule of thumb, if a manufacturer is unwilling to identify the grade of stainless used, then it’s probably a cheaper grade that’s less corrosion-resistant. (Fun fact: During the Cold War between the US and Russia, the KGB caught American spies because their fake passports used pricier, stainless steel staples that would not rust, unlike like Russian staples.3)
Lastly, avoid Indian stainless steel. Indian stainless is usually low-grade and will rust more easily, which is why you almost never see a grade (e.g., 18/10 or 18/8) stamped on Indian stainless. Furthermore, India is even worse than China when it comes to blending radioactive scrap metal into their steels. In fact, radioactivity has been detected in everything from elevator buttons to belt buckles, stainless steel pet food bowls, cutlery, furniture, hand tools, and tissue paper boxes. I’ve tested al of my kitchenware with a geiger counter (the good kind, with alpha, beta, gamma detection capability), and I haven’t found anything abnormally radioactive yet. So don’t worry too much about radioactive cookware for the time being. But rest assured I will report the news if I ever come across a “hot” object.
There are only a few common ways to damage stainless steel. One way it to use chlorides, usually salt or bleach, which can prevent the chromium oxide protective layer from forming. This results in pitting (localized corrosion). Never use bleach to clean stainless steel, or if you must, then quickly and thoroughly clean it with water. Similarly, avoid storing very salty or acidic foods like vinegar or tomato sauce in stainless steel. An hour or two is fine; overnight is not. Conventional wisdom is to add salt to pasta only when the water is boiling and thus churning and spreading the salt around, so that you don’t run the risk of having high concentrations of salt at the bottom of a pot.
It is possible to use steel wool on stainless steel cookware. It may result in ugly scratches and disruptions of the chromium oxide protective layer, but as long as you wash and rinse, another protective layer will form. To avoid ugly scratches, use nonscratch (e.g., Blue Scotch-Brite) sponges and wooden, nylon, or silicone utensils. Note that even if you only use nylon or wooden or silicone utensils, scratches are inevitable–somewhere along the line, a bone or something else in the food itself will scratch up the stainless. It won’t affect cooking performance, just looks. Personally I try to avoid using steel wool simply because I want to extend the life of my pans and avoid the ugly scarring.
High heat can turn stainless steel into a rainbow of hues. Extremely thin layers of cooked-on oil will also give you rainbows.4 Thin layers of hard water and food stains such as protein residues may add to the rainbow or else make the steel look duller or cloudy. None of these stains affect cooking performance or sanitation because the layers are so thin and were burned on at such high temperatures that bacteria did not survive, so don’t feel like you need to clean your stainless steel pans to “like new” condition after each cooking session. In fact, the next time you cook acidic food in the cookware, the acids in the food will naturally lift some or all of those stains away. If you can’t wait that long, just use a little Bar Keepers Friend and rub the stains off.
If you REALLY overheat stainless steel, such as by accidentally letting something boil dry and allowing the temperature to soar well beyond 500F (something I am guilty of doing accidentally to one of my poor Cuisinart MultiClad Pro pots), then stainless will take on a yellowish tinge. Don’t panic. Over time, the oxidized yellow tinge will come off with wear and tear. If you can’t wait that long, then as soon as reasonable after cooling down the overheated cookware, take some Bar Keepers Friend and rub as much yellow off as you can.
If you are used to cooking on nonstick (PTFE such as Teflon), then stainless steel may seem sticky. To minimize stickiness, follow this order of operations:
1. Heat the pan to frying temperatures. What that means depends on what you’re trying to fry and what oil you’re using; you want to stay below the smoke point of the oil. Extra virgin olive oil has a smoke point of around 360-400 degrees F depending on various factors like impurities.5
a. For best results, you don’t want ANY part of the pan to exceed the smoke point of your oil. The higher-ranking your cookware in terms of thermal conductivity, the more evenly your cookware will heat up and the less likely you will have a burner-shaped hot spot. Low-ranked cookware like cast iron heats unevenly, so preheat cast iron on low to medium-low heat to give the pan time to spread heat around the bottom of your pan. (Exact settings will vary; what is “low” on one stove might be “medium” on another.)
b. If you’re having trouble figuring out the right temperature, do this: flick water onto the pan. If the water fizzles without moving much, the pan isn’t hot enough. If the water droplets keep r0lling around the pan as if they were hockey pucks on ice, then your pan is 400F+ (each droplet is floating on a thin film of water vapor; this “Leidenfrost effect” occurs around 400F/200C at sea level). Turn down the heat to “low” and also take your spatula and push the water into the pan to force it to evaporate. (If you don’t smash the water, it may mix with hot oil and splatter onto your clothes.) While this is going on, your pan will drop from 400F+ down to something hopefully lower than the smoke point of whatever oil you’re using.
2. Add oil and wait for it to start shimmering. (Some people prefer to add oil to the cold pan and preheat the pan and oil at the same time, but in my experience it doesn’t always work as well as preheating the pan and then adding oil.) Do not let the oil start smoking, as it is giving off carcinogens at that point. Turn down the heat if you haven’t already, and add food. How much to turn down the heat varies by stovetop and cookware; try lowering heat to “low” as a first attempt and then work up or down from there. You might have to leave it on medium or even high heat if you are trying to cook a cold, thick steak.
3. Proteins will stick and then release on their own after a few minutes. Eggs and fish remain some of the trickiest foods to cook with stainless, and you may have to resort to using more oil/fat than usual, and a tighter control of heat than usual, for those foods. Eggs, for instance, do not need to be cooked at high heat, so I would recommend preheating the pan, adding oil, and then turning down the heat to the lowest level you can get away with and then slowly and gently cook the eggs.
4. After cooking, you can deglaze the pan with wine, water, or something else to make a pan sauce or gravy to go with whatever you just cooked. This also helps with cleanup. (Deglazing just means adding a little liquid to a pan with stuck-on bits. The resulting liquid is often packed with delicious flavors and can be used in gravy or something else.)
Some people are worried about iron, nickel, chromium, or something else leaching into food from stainless steel, but the amounts are so minute as to not matter unless you are allergic to nickel. Your body needs some amount of chromium to be healthy, anyway. Furthermore, the kinds of compounds that those elements make are unlikely to harm you. The only people who need to worry about cooking with stainless steel are those with significant nickel allergies.
- http://www.atsdr.cdc.gov/toxguides/toxguide-15.pdf See also http://fses.oregonstate.edu/node/440 ↩
- The clip weighs 4.3 grams. Nickels weigh 5 grams each. I weighed zip-loc bags contain 2, 4, and 20 nickels. They weighed 12.2, 22.2, and 102.2 grams, so obviously the zip-loc bags each weighed 2.2 grams. Therefore I tested four combinations of weight, using 2, 4, 6 (2+4), and 20 nickels: 16.5, 26.5, 38.7, and 106.5 grams. That’s 0.58, 0.93, 1.37, and 3.76 ounces, respectively. (1 ounce = 28.3495 grams = 1/16 of a pound) ↩
- http://news.bbc.co.uk/2/hi/europe/2065020.stm ↩
- http://articles.baltimoresun.com/2006-03-29/news/0603280034_1_stainless-steel-all-clad-cookware-oxalic “Groll (All-Clad scientist) said your “rainbow” stains are actually very thin layers of caramelized oil. Like a glass prism, the oil refracts light at different angles, causing a rainbow effect. The cloudy stains, he guessed, are probably protein residue.” Erica Marcus, for Newsday, reprinted by Baltimore Sun, March 29, 2006. ↩
- Do not use an infrared thermometer to take the temperature of shiny pans while preheating. Most affordable IR thermometers are preset to emissivity 0.95 which is a far cry from the emissivity of shiny stainless which is around 0.10. You can use IR guns on cast iron or ceramic, though you will still overshoot somewhat. ↩