The right alloy for catering and preservation
Machines and equipment used in the canning industry, as well as those used in the catering industry, must guarantee very high hygiene standards. Due to its immutability, stainless steel is almost always the mandatory choice for these areas. Each alloy has its own advantages and disadvantages, which requires careful selection among the hundreds of variations of this material.
There is therefore no single answer to the question of “which stainless steel is best” in the catering and food industries. Making sweets is not the same as making cheese: the temperature used changes and, most importantly, so does the chemical composition of the processed food. In the canning industry, the most commonly used alloys are AISI 316 and AISI 430.
AISI 316 stainless steel
316 is an austenitic stainless steel with a high chromium and nickel content. Like almost all metals, it has a higher temperature range of use than that of food preparation.
This steel is particularly suitable for contact with foodstuffs because of its high resistance to acids, alkalis and chlorides (e.g. salts). Other austenitic stainless steels (e.g. 304) can form severe pitting corrosion. 316 is immune to this type of corrosion and for this reason it is suitable for almost all applications.
AISI 430 stainless steel
From a metallurgical point of view, AISI 430 stainless steel is very similar to 316. It has the same chromium content, but has a lower nickel content, which is what makes it less expensive.
Another important difference is that AISI 430 is a ferritic alloy, which means that it is magnetic. Ferritic alloys have a very high resistance to low stress corrosion cracking, i.e. the formation of cracks in the presence of mechanical stress in a corrosive environment.
430 stainless steel also has excellent resistance to organic acids and nitric acid, so it can be used in contact with acidic foodstuffs.
It has excellent resistance to oxidation and sulphur-containing substances. On the other hand, due to its low nickel content, this alloy is not very reducible to the acids contained in certain foodstuffs.
Which are the best steels for food?
Generally speaking, AISI 316 is the best choice for machinery and containers for the canning and catering industry. Its ability to resist salt and acidic foods, such as tomatoes and citrus fruits, makes it an excellent material. For less critical applications, AISI 430 can be a cheaper but equally effective compromise.
Whichever alloy is used, it is important to use a low roughness surface finish, such as that obtained by polishing or electropolishing. The elimination of fine particles reduces the risk of cracking and corrosion and makes cleaning easier.