Many times we will have read in one of our analyses of coffee machines or in some instruction manual that this or that product is built with 18/10 stainless steel. But, do consumers know what they are buying? Do we know the difference between 18/10 and conventional steel? In this article, we will try to clear up doubts, clarify concepts and review what relationship this material has with our world: that of domestic coffee machines.
The 18/10 stainless steel is a special type of stainless steel composed of a steel alloy with exactly 18% chrome and 10% nickel. Other stainless steels (we will review all the existing ones later on) can have in their alloy chromium proportions of 17%, 19%, 20% or even higher. The minimum to achieve stainless properties is 12% chrome.
This 18/10 stainless steel acquires very beneficial properties for the treatment of food and uses in the kitchen. It is much more durable, more resistant to temperature changes and friction, and does not release any substance.
It is therefore very suitable for contact with food. For this very reason, it is widely used in the manufacture of kitchenware, and in particular in the construction of coffee machines.
304 stainless steel vs. 316 stainless steel
Unfortunately, the information provided by coffee machine manufacturers is often incomplete or deficient and does not always specify what kind of stainless steel has been used in their product. To clear up any doubts, we can also look at their AISI nomenclature.
The 18/10 stainless steel corresponds to the AISI 304, while the more conventional stainless steel (of those used in the food industry) is known to the AISI 316 standard. As we have said, the normal thing in a kitchen utensil is to use either 18/10 stainless steel (AISI 304) or 316 stainless steel, but we cannot be sure if the manufacturer does not indicate it in the standards or the user’s booklet.
NOTE: AISI stands for American Iron and Steel Institute.
To confirm it, we can also go to the following comparative table, where we can check the chemical composition of each type of stainless steel. As you can see, the highest percentage in the alloys corresponds to nickel and chromium.
The differences between 304 and 316 stainless steel are negligible to the naked eye. Both 18/10 stainless steel (AISI 304) and AISI 316 are processed, polished, crystallized and finished in the same way.
If we go into the composition report, we see then that the stainless steel 304 does not contain molybdenum, while the stainless steel 316 contains 2% of molybdenum. This subtle difference completely transforms the use and purpose for which the product made of this material can be used.
You see that without a table of equivalence of stainless steel, it is sometimes difficult to distinguish which we are.
Cromargan stainless steel
The stainless steel 18/10 Cromargan is a special type of steel, widely used by the German manufacturer WMF in the finishes of all its articles. Its composition is 72% Steel, 18% Chrome, and 10% Nickel.
In theory, Cromargan steel is much less porous than conventional steel, and therefore less subject to the release of heavy metals in contact with food. The Teutonic firm itself defines it as a “stainless steel alloy with a special 18/10 ferrous combination” and assures that it is easier to clean and more inalterable over time.
18/10 Stainless steel in the construction of coffee machines
It is also important to distinguish between the different areas where stainless steel can be used in a coffee maker. The surfaces that are in direct contact with the food (for example, the boilers with the water in the espresso machines or the interior of the Italian coffee machines) could be built with 18/10 steel because that is where its benefit is noticed.
Something else different is the stainless steel coatings, trims, or finishes that are used on espresso machines to decorate them or to make their external casing more solid.
In the latter case, the steel never comes into direct contact with any food or coffee, and therefore it is not so important whether it is 18/10 or conventional stainless steel, beyond the question of wear and tear.
18/8 Stainless steel
The 18/8 stainless steel is another of the most used commercial alloys because it resists very well high temperatures (up to 400ªC). Its composition is 18% Chrome, 8% Nickel (as indicated by its nomenclature) and 0.18% Carbon. It has a mechanical resistance of 60 kg/mm² and a hardness of 175 to 200 HB.
Types of stainless steel
The list is so extensive that we cannot accommodate it on this page; it would not make sense. So until now, we have focused mainly on the types of stainless steel used in the food industry. That is, those that are considered most suitable for contact with food.
But, beyond the one used in the construction of coffee machines and other kitchen instruments, there are numerous types of stainless steel, usually classified according to the alloy or mixture of components they contain (and their proportion, above all).
What other types of stainless steel are there? Well, we summarize them in this list:
- Martensitic stainless steels: They are chrome and carbon alloys. They represent a section of the 400 series of steels, and are magnetic, corrosion-resistant and very little weldable.
- Ferritic stainless steels: They belong to the 400 AISI series. The chromium content in these steels is 10.5% to 30%. They have no more than 0.08% carbon, and are very little hard. Poor weldability, very soft, ductile and magnetic.
- Austenitic stainless steels: Series 200 and 300 AISI. They are very resistant to corrosion, very weldable, extremely hygienic and are not magnetic. Chromium is present in values from 16% to 26%, while carbon never exceeds 0.08%.
- Duplex stainless steels: are alloys of chromium, nickel and molybdenum. Magnetic, good weldability, and very resistant to corrosion, although they cannot be hardened by heat treatment. The chromium content varies between 18% and 26%, and the nickel content between 4.5% and 6.5%.
Stainless steel qualities
Derived from the previous section, more than talking about the qualities of stainless steel, we should talk about its composition and the use it will be given. Good steel for construction can be not suitable to elaborate kitchen instruments, and that does not mean that one necessarily has more quality than another, simply that its composition is more oriented to favour some properties or others.