The short answer is that not all stainless steel is made the same way, and as a result some is considered safer than others. Craig Stellpflug, who is identified as a cancer nutrition expert, explains that “Stainless steel cookware is made from a metal alloy consisting of mostly iron and chromium along with differing percentages of molybdenum, nickel, titanium, copper and vanadium. But even stainless steel allows other metals to leach into the foods. The principal elements in stainless that can have negative effects on our health are iron, chromium and nickel.”
When you look at stainless steel cookware, you’ll see numbers such as 18/0 and 18/8 that refer to the percentages of chromium and nickel in the stainless steel alloy. The “18” refers to the chromium content, which gives flatware its rust-resistance properties, and the “8” or “10” refers to the nickel content, which gives it its silver-like shine and some rust-resistance. 18/8 and 18/10 are the most common types used for stainless steel cookware and food applications. According to the National Institute of Health (NIH), safe dietary intake of chromium for adults and adolescents is 25 to 45 μg per day. However, there is no Tolerable Upper Intake Level (UL) set . The chromium in solid stainless is not to be confused with Chromium 6. Chromium 6 (hexavalent chromium) is a carcinogen that is given off in fumes during the welding of stainless steel, but our kitchen stoves cannot cause stainless steel to break down to this level.
As John Moody points out “… the health risks from the nickel are worse than from the chromium. For this reason, it is best to stick with higher chromium stainless steel cookware. Our body needs chromium albeit in small amounts. There are also many biological defenses against excess intake.”
According to numerous sources, the safest stainless steel to cook with is nickel free or 18/0. The outside layer of Gunter Wilhelm cookware is made from type 430 stainless steel. This kind of stainless steel material contains a minute amount of nickel (0.50 percent or less). Also Homichef makes a food grade nickel free stainless steel (21/0) which is labeled as non-toxic, and non-allergic. The 6-piece set I link to is sold on Amazon at a 37% discount.
Update – I had a follow up question that prompted me to add this information: Ted Mooney explains that the differences between 18/10, 316, 316L, and 316Ti are subtle and minor. Saladmaster is made from 316Ti, which still contains nickel. Also, I just found another couple more cookware options that are 18/0: Jarhill and Faberware. I spoke to a representative at Faberware and he said that the current products are 18/0 stainless steel. No nickel. So it depends on what version you have. Look on the outside botton of your pot. If it says 18/0 or durable, there is no nickel, otherwise it will either say 18/10 or aluminum clad and that would pertain to the older products that do contain nickel. So in summary:
Non-Nickel Stainless Steel Cookware:
Very low-nickel: Gunter Wilhelm
Another Update! September 28: I called Saladmaster today and spoke to a representative. She said they don’t share their names when I asked for hers – (817) 633-3555 Option 4. She confirmed Saladmaster does contain 16% to 18% chromium and 10% to 14% nickel, and is more stainless steel than titanium. Titanium content is typically only around 0.5%, as you’ll see in this document she emailed me. I asked her if they had any research on the product materials leaching into food and they do not. I summarized this study. She said that even with the Saladmaster, with extensive exposure to acid foods, and/or salt, prolonged use can create pitting in the metal. I explained that we recommend folks add vinegar to the bones used to make broth to draw out the minerals, and folks likely add salt as well for flavor. I said my perspective is that bone broth simmered in stainless steel for 12 to 72 hours may not be the safest cookware option. I asked her if that sounded like a reasonable statement to her and she said “yes, it does!” I personally think that the very safest way to make broth is in non-metal cookware.
When it comes to cookware, I err on the side of caution. I don’t use or recommend the Instant Pot because I am not drawn to the high heat and high pressure of the pressure cooker feature. I also would not use it as a slow cooker because the inside part is made with 18/8 stainless steel. That means that it is 8% nickel. Metals are found to leach into food cooked in stainless steel, according to research published in the Journal of Agricultural and Food Chemistry:
After a simulated cooking process, samples were analyzed by ICP-MS for Ni and Cr. After six hours of cooking, Ni and Cr concentrations in tomato sauce increased up to 26- and 7-fold respectively, depending on the grade of stainless steel. Longer cooking durations resulted in additional increases in metal leaching, where Ni concentrations increased 34 fold and Cr increased approximately 35 fold from sauces cooked without stainless steel.
Cooking with new stainless steel resulted in the largest increases. Metal leaching decreases with sequential cooking cycles and stabilized after the sixth cooking cycle, though significant metal contributions to foods were still observed. The tenth cooking cycle, resulted in an average of 88 μg [micrograms] of Ni and 86 μg of Cr leached per 126 g serving of tomato sauce. Stainless steel cookware can be an overlooked source of nickel and chromium, where the contribution is dependent on stainless steel grade, cooking time, and cookware usage.
Many in our community use the Instant Pot to make broth in. Our recommendation is to add vinegar to the broth to draw out the minerals from the bones. As John Moody asserts: “For longer cooking and acidic foods, such as tomato based sauces or slow simmering of stocks, use alternate cookware. Safe options include certified toxin free clay pots, such as Vita-Clay, glass, or ceramic coated cast iron. While convenient, stainless steel pressure cookers are not ideal for cooking these items.”
As I said, I don’t use or recommend an Instant Pot; especially not for broth. I use a Hamilton Beach crock pot to make broth in, as well as a stainless steel stock pot that passed the stainless steel magnet test explained below. Before you ask, I am not concerned about lead in this crock pot. In addition, see this article from the Lead Safe America Foundation. I also use a Le Creuset stock pot for broth.
Acidic Foods and Beverages
John Moody also points out that “Bottled store kombucha, an acidic beverage, is typically brewed in large stainless steel vats. It is best to avoid commercial kombucha for this reason. Be sure to brew kombucha or Jun tea in glass or tested, toxin free ceramic when made at home. Store these beverages only in glass as well.”
How do we know if there is nickel in our stainless steel cookware? Copied from my cookware recommendations article:
Stainless Steel Magnet Test
There are two main types of stainless steel, magnetic and nonmagnetic. The nonmagnetic form has a very high nickel content, and nickel is allergenic and carcinogenic. It is much more toxic than iron or aluminum. You can use a little “refrigerator magnet” to test your pans. The magnet will stick firmly to the safer type of pan.
It is wise to use the magnet all over the pan – inside and outside since some have found that the pan contains mixed ingredients and sticks firmly in some places and not in others.
Scratched or Damaged Stainless Steel
Also, keep in mind that aluminum is sometimes placed in between stainless steel layers in stainless steel cookware. So if your cookware becomes scratched or damaged in any way, including rust, aluminum may leach into your meals as well. I would recommend you recycle stainless steel that may pose that risk.