Stainless steel in kitchen utensils is one of the most widely used materials, both at a domestic level and in professional restaurants, as well as at an industrial level.
This is mainly due to three characteristics of stainless steel:
- It is mechanically resistant
- It is resistant to chemical corrosion
- Can be easily cleaned, sanitized, and sterilized
There are many types of stainless steel with different compositions and properties. Which is often a source of confusion and also a concern when choosing stainless steel cooking utensils for our kitchen.
Throughout this article, we are going to define what exactly stainless steel is and what types there are. We also discussed, what are its most common applications in the kitchen, as well as its composition and possible interactions with food and health.
What is stainless steel?
Image Source: https://en.wikipedia.org/wiki/Stainless_steel
Stainless steel is a term that designates a whole family of iron alloys characterized by their more excellent resistance to corrosion and high temperature compared to pure iron and other types of steel and alloys. The main elements in stainless steel are iron(Fe) and chromium(Cr). According to the International Stainless Steel Forum, the minimum chromium content must be 10.5%, although the exact amount varies greatly depending on the specific type of stainless steel.
In addition, like all steels, stainless steel always contains carbon up to a maximum of 2%.
Other elements, such as nickel, molybdenum, or nitrogen are also added to improve corrosion resistance, mechanical strength, or other properties, such as malleability or weldability.
What makes stainless steel corrosion-resistant?
The resistance to corrosion and oxidation of stainless steel is due to the phenomenon of passivation, that is, the formation of a protective film on its surface that protects it from external agents.
This film is composed of chromium III oxide (Cr 2 or 3 ). Which is formed when chromium reacts with oxygen and humidity in the environment. That’s why it is said to be a passive process since it does not require a directed action during its manufacture for it to form. From 10.5% chrome, the protective film formed covers the material’s surface homogeneously with a thickness of 2-3 nm, enough to protect the iron from oxidation.
A very important feature of this protective layer is self-healing. Where the stainless steel becomes exposed again, and the chromium III oxide layer forms again. The passivation process also occurs in other corrosion-resistant metals. For example, it occurs in titanium with the formation of titanium oxide. The corrosion resistance of stainless steel is improved by increasing the chromium concentration and adding other elements to the alloy.
For example, the addition of nickel above 8% considerably improves resistance to corrosion in general, especially acid and salt corrosion, while molybdenum above all improves resistance to pitting, a very localized type of corrosion.
General Stainless Steel Categories
The different types of stainless steel are classified into four large families based on the structure or metallographic phase observed at the molecular level:
- Austenitic stainless steel: Its molecular structure corresponds to austenite (iron + carbon alloy). It is the most important for the family by production and use. They are the most resistant stainless steel to oxidation, corrosion, and temperature, especially due to the addition of nickel. It does not present magnetism.
- Ferritic stainless steel: Molecular structure of ferrite. This stainless steel has little or no nickel is less resistant to corrosion than austenitic, and exhibits magnetism.
- Martensitic stainless steel: Molecular structure of martensite (the result of rapid cooling of austenite). It is the hardest and most mechanically resistant stainless steel. But with lower corrosion resistance. Like ferritic, it exhibits magnetism.
- Duplex stainless steel: Mixed austenitic and ferritic structure. It has magnetism.
Types of stainless steel
Within each household, an idea can be created with the composition, properties, and qualities of stainless steel. an infinite number of types or grades of stainless steel that are chosen according to the specific applications.
There are numerous grading systems for stainless steel. The most widely used is the SAE numbering system, which is maintained and developed by SAE International, and the European standard EN 10088 (5). Although there are many more, for example, the JIS and NK standards from Japan, and numerous standards ISO that refer to elements made of stainless steel.
The SAE system was originally developed jointly by the SAE (Society of Automotive Engineers) and AISI (American Iron and Steel Institute). It is still common to see AISI or AISI/SAE numbering, considered equivalent.
In the SAE system, each grade of stainless steel is given a 3-digit number. It currently has more than 150 grades of stainless steel grouped into several series:
- 100 Series – General purpose austenitic stainless steel. It is not very common at a domestic level, except for 102, which is widely used in low-quality furniture and decoration.
- 200 series – Austenitic stainless steel made from chromium-nickel-manganese alloys. They offer moderate corrosion resistance. Grade 201 is used relatively frequently in food containers.
- 300 series – low manganese austenitic chromium-nickel alloys. It includes grades 304 (stainless steel 18/10 and 18/8) and 316, the most used in the kitchen.
- 400 Series – Ferritic and martensitic alloys that use little or no nickel. Of these, the 430 and 440 are widely used in cutlery and also frequently in sinks, countertops, and other kitchen applications.
- Others: (1). 500 series (nickel-free, low chrome, high heat resistance, less corrosion). (2). 600 series (currently excluded from SAE standard). (3). 900 series (adds more chrome and more molybdenum for increased corrosion resistance ).
The stainless steel used in kitchen utensils
According to the NSF International Standard for Food Equipment Material, stainless steel in contact with food must have a minimum of 16% chromium by weight and must belong to the SAE 200, 300, or 400 series.
The most widely used of all is SAE 304, with two subtypes, 18/10 and 18/8, which indicate the chromium and nickel content: 18% chromium and 10 or 8% nickel, respectively.
201 stainless steel
The SAE 200 series is mainly characterized by containing manganese to replace part of the nickel. It is usually cheaper stainless steel and less resistant to corrosion and temperature.
Within this group, the most widely used in stainless steel cooking utensils and food applications is SAE 201 (EN 1.4372). Especially in lunch boxes, food containers, and the like, in which their use does not imply any risk of corrosion. It can also be found in equipment and other types of kitchenware.
304 stainless steel: 18/10 and 18/8 plates of steel
SAE 304 stainless steel (EN 1.4301) is the most widely used of all stainless steel, not only in the kitchen but also in any other application.
There are several subtypes of 304 steel that, are usually designated by two numbers based on their chromium and nickel content:
- 18/10 stainless steel: contains 18% chrome and 10% nickel.
- 18/8 stainless steel: 18% chrome and 8% nickel.
Although in practice we may not notice a difference, 18/10 stainless steel is considered to be of higher quality, greater resistance, and greater durability.
It is used for every conceivable application in the kitchen, hospital, restaurant services, and the food industry: cutlery, pots and pans, cookware, countertops, all kinds of electrical appliances and machinery, and much more.
Pots and pans made with this type of stainless steel usually have an aluminum core. Sometimes copper allows even heat distribution since stainless steel alone does not do it well.
316 stainless steel, surgical steel, and titanium reinforced
SAE 316 stainless steel (EN 1.4401) is the second most widely used type of stainless steel of all. It is similar to 304 but contains molybdenum, which gives it greater resistance to corrosion, especially acid corrosion, chloride corrosion, and pitting. Generally considered to be of higher quality than 304, the most prevalent in high-end cookware and batteries.
We can also find the 18/10 numbering in 316-grade stainless steel. But we have to be clear that 316 grade is more expensive than 304, considered to be of higher quality. If they only give us the 18/10 numbering without saying anything else, most likely grade 304. Within 316 stainless steel, there are several subtypes. Of these, SAE 316Ti (EN 1.4571) is reinforced with titanium and is used in high-end pans, pots, ovens, and other cookware. Although the amount of titanium that is added is very small (less than 0.70%), it considerably increases long-term corrosion resistance, especially for continuous use at high temperatures, by reducing the formation of chromium carbide (Cr 3 C2 ).
316 steel is also used in medical applications. Hence, it is known as surgical steel, almost always referred to as subtype 316L (low carbon, EN 1.4404 with 2% Mo and EN 1.4436 with 3% Mo). Although this denomination is used often as a claim for other grades of stainless steel, so always check the standard used and not get carried away by these generic names.
“Nickel-free” stainless steel
Nickel-free stainless steels belong to the SAE 400 series. A key difference to differentiate it from the others is that being from the ferritic and martensitic families, it exhibits magnetism. Within this series, the most common in the kitchen is SAE 430 (EN 1.4016, ferritic type). It is also designated as 18/0 stainless steel (18% chrome, 0% nickel). However, the 18/0 designation is misleading, as 430 steel contains up to 0.75% nickel.
18/0 stainless steel is very common in mid-range cutlery, the most common in any home. Since it is usually cheaper than 18/10 and 18/8, it is not necessary to stabilize the alloy to resist high temperatures. If your cutlery has magnetism, it is of this type. Higher-end stainless steel cutlery is usually made from 304 18/10 or 18/8 steel. 18/0 steel is also very common in countertops and preparation surfaces. It is much less resistant to corrosion than 18/10 and 18/8.
We can also find cutlery made of 13/0 stainless steel, which usually corresponds to SAE 410 and also has 0.75% nickel or SAE 420 grade. In both cases, due to their low chrome content, this cutlery has a very low resistance to corrosion, which is why they are considered the lowest quality. Even, if it does not reach the minimum 16% chrome mark set by NSF International.
Another type of nickel-free stainless steel that we can find in cookware is SAE 440, especially subtype 440C (EN 1.4125, martensitic type), sometimes called ” Japanese steel “. It contains more carbon than other stainless steel and is highly resistant to wear. We find it in professional and high-end cutlery, as well as in industrial cutting machinery since they stay sharp longer. So again, it is always advisable to check the standard used and not be carried away by generic names.
Heavy metal release and safety of stainless steel in cookware
Stainless steel is considered a biologically inert material. Generally safe to cook with it. although, it is well known that it can release elements like chromium and nickel into food under certain conditions.
Of these two elements, chromium is an essential nutrient for humans. Men and women need to take 35 and 25 μg recommended daily, respectively. All its functions or mechanism of action are not exactly known. It often interferes with the metabolism of lipids and carbohydrates, and its deficiency causes glucose intolerance.
However, of all the forms of chromium, the one that is considered an essential nutrient for humans is Cr III (oxidation state +3). Cr III is present in numerous foods and is the one formed in stainless steel during passivation, as described above. For its part, Cr VI is highly oxidative and carcinogenic. The presence of Cr VI in nature comes mainly from industrial pollution, especially from the oil industry.
For its part, nickel is not a nutrient for humans, although it is for many other forms of life, including plants, bacteria, archaea, and fungi. For example, nickel is essential for urease ( EC 184.108.40.206 ), an enzyme used by many types of bacteria, including many of the species of our intestinal flora. In this sense, nickel could even be considered a prebiotic.
However, although both elements must be present in our diet in one way or another, the amount we need is really low. Both metals can trigger allergic reactions, especially dermatological, in sensitive people. Many studies on the release of these metals from stainless steel in cookware use unusual cooking conditions. It would be truly unusual in everyday life.
Other studies were conducted under typical conditions of use. The release of nickel and chromium from stainless steel in cookware into food triggers allergic reactions. At the same time, it is considered below safe limits. In all cases, it has decreased drastically after the first cycles of use.
Another frequent concern about chromium and nickel is their endocrine-disrupting effect and the additive effect due to accumulation in fatty tissue. Similarly, this effect on chromium is for Chromium VI and not for Chromium III or metallic chromium. Nickel is also related to several forms of cancer, especially lung cancer and nasal cancer.
But the relationship between these effects, and exposure from food use of stainless steel, both domestically and industrially. It has not been firmly established with currently available data, only in work settings where exposure is much higher and is produced by by-products derived from stainless steel. For example, these metals have very high levels of exposure due to exposure to the vapors provided by stainless steel during casting, or to environmental pollution.
In general, it can be concluded that stainless steel in kitchen utensils is a safe material for food use, including pans, and pots. Also, safe other applications that are going to be subjected to high temperatures. It should only be avoided in case of allergy to nickel or some syndrome of sensitization to these metals.
Although avoiding it completely, is going to be almost impossible, because it is a material that is practically universally used in the food industry, hotels, and restaurant services. As we have mentioned, the release under normal conditions of use should not worry us.
How to care for stainless steel kitchenware?
To take care of kitchen utensils and appliances made of stainless steel, maximize their durability, and minimize the release of metals.
A series of recommendations can be followed:
- Never clean stainless steel kitchenware with corrosive substances such as bleach (sodium hypochlorite), very acidic substances, such as strong water (hydrochloric acid), or the opposite, very basic or alkaline substances such as ammonia or caustic soda (hydroxide) of sodium. Even the vapors given off by these substances can considerably affect stainless steel.
- Scrub stainless steel cookware with non-abrasive scouring pads and in the direction of polish lines if they are visible.
- Let pots or pans cool before cleaning them. Never cool stainless steel utensils abruptly by immersing them in cold water.
- Although stainless steel is very resistant and does not scratch easily. The use of highly abrasive pads, such as metal scouring pads, should be avoided. If there is hardened or difficult to remove dirt, it is better to soak it and use a soft scourer.
- When cooking, the most important thing to take care of is stainless steel to avoid excessive and unnecessary heating. For example, avoid heating without food or liquids (eg: boil water, forget about it, and let it be consumed). You should also avoid preheating too quickly since stainless steel retains heat very well. There is a risk of overheating pots or pans, damaging them, and also burning the food.
- Cutlery and other kitchen utensils damaged or with signs of deterioration must be discarded and deposited in the clean points of your locality for their correct recycling and treatment. It is not recommended to dispose of them with the rest of the general garbage.
Of all the metallic alternatives for the kitchen that we currently have, stainless steel is one of the best due to its mechanical resistance, resistance to chemical corrosion, temperature resistance, and easy cleaning and sanitizing.
Although there is concern about possible toxicity from the release of metals into food, under normal conditions of use this should not be cause for alarm.
What you do have to be clear about is always choosing the highest quality stainless steel and using it appropriately.
- 316 stainless steel would be the highest end, especially 316Ti which is reinforced with titanium.
- 18/10 (grade 304) stainless steel for high-quality cookware. It should be the minimum acceptable for cookware (pots, pans, etc).
- 18/8 (grade 304) stainless steel is suitable for high-quality flatware and food and beverage containers.
- 18/0 stainless steel (grade 430) is the most common in household cutlery. It is considered mid-range cutlery due to its lower corrosion resistance. In any case, avoid 13/0 stainless steel cutlery.
- 440 stainless steel is the one chosen in professional cutlery for its great hardness and mechanical sharpening resistance.
- 201 stainless steel may be suitable for lunch boxes and similar containers. It is the minimum, that meets the NSF International standard for kitchen and food contact stainless steel.
Frequently asked questions about stainless steel in cookware
Is it healthy to cook with stainless steel?
Stainless steel is an alloy of metals, some of the heavy metals that are toxic to our bodies. However, the release of these metals into food when cooking with stainless steel occurs at very low levels, even below levels that cause allergic reactions. Stainless steel should only be avoided in the kitchen in case of allergy to nickel or sensitization syndromes to any of the metals that make up stainless steel.
Is stainless steel a good thermal conductor for cooking?
Stainless steel is not a good thermal conductor. So the quality of stainless steel kitchenware usually has a diffuser bottom, usually with aluminum inside.
What is the best stainless steel for cooking?
Type 316 stainless steel or surgical steel is the best quality for cooking. Because it contains molybdenum in its alloy, making it more resistant to corrosion. Followed by type 304 stainless steel, which includes 18/10 and 18/8 stainless steel.
What is 304 stainless steel?
It is the most common steel in the kitchen, also called 18/10 stainless steel and 18/8 stainless steel. 304 stainless steel includes steels that contain between 18 and 20% chromium and between 8 and 10.5% nickel.
What is 18/10 stainless steel?
It is stainless steel that contains 18 parts chromium and 10 parts nickel (also called 304 stainless steel). It is one of the most used stainless steel in the kitchen along with 18/8 steel, stable, and with good corrosion resistance.
What does 18/8 stainless steel mean?
It is stainless steel that contains 18 parts chromium and 8 parts nickel (also called 304 stainless steel). It is one of the most used stainless steels in the kitchen along with 18/10 steel, stable and with good resistance to corrosion
What is 316 stainless steel?
It is the most common stainless steel in the kitchen after 304. It contains molybdenum, which makes it more resistant to corrosion. Surgical steel is a type of 316 steel.
What is surgical steel?
It is stainless steel with molybdenum, which makes it more resistant to corrosion. It is also called 316 stainless steel.
What is stainless steel with titanium?
It is 316Ti stainless steel. 316 steel or surgical steel contains molybdenum to make it more resistant to corrosion. Titanium is also added to 316Ti steel, in a very low percentage, less than 0.7%. In kitchen utensils, this addition of titanium in stainless steel does not represent any advantage.
Why doesn’t stainless steel rust?
Stainless steel is an alloy of iron with other metals, therefore it should rust due to its iron content. But the chromium it contains in its mixture gives rise to the formation of a thin protective film on its surface. Which protects it from external agents due to a chemical process called passivation.
Why do stainless steel pots chip?
When spots of corrosion appear on the surface of a stainless steel pot, it is because it has a chromium content of less than 10.5%.
Can I recognize stainless steel by doing the magnet test?
No, this test which is often done to check the magnetism of stainless steel to recognize if a metallic material is stainless steel or not, is not valid. Not all steels are magnetic. since austenitic steels, although they contain iron, do not have magnetism due to the molecular arrangement of iron when mixed with carbon.