Metals for Food Processing
As with all great discoveries the invention of stainless steel was almost missed. It is purported that Brearley, who became Head of Research at Firth Brown Steels, Sheffield, was experimenting with different types of chromium and carbon levels, based on a ratio of 0.24wt% C, 12.8wt% Cr ferrous alloy, which led him to the discovery of stainless steel.
Initially discarded alongside various other test materials Brearley noticed that a couple of days later this particular alloy hadn't oxidised like the others, it had "stained less". Further testing proved the alloy to be resistant to acids, vinegar and lemon juice and with Sheffield recognised during that era as the most important cutlery making centre in Britain, Brearley quickly realised that this particular metal alloy would be ideal for the cutlery industry. Today due to the steel's propensity for being highly corrosion resistant and dish washer safe it has become a staple of the cutlery trade worldwide.
The grades of stainless steel and the industries which use it are vast. The most popular grade of steel within the food processing industry is 304 but the choice of which grade to use will depend upon the final application. Martenistic steels find their way into the pumps and kitchen knives whereas ferritic grades are better suited to appliances like fridges, dishwashers and saucepans. Stabilisation through the additions of molybdenum, niobium and titanium give the material differing properties enabling engineers and designers to choose the most efficient for the purposes they have in mind. For instance a 304 stainless grade containing an addition of 2% molybdenum would increase its resistance to pitting making it useful in containing salty foods.
The ductility of high nickel content austenitic grades make them the choice of the food and drink industry as they offer good corrosion resistance and are easy to roll, draw and press into shapes. We see its use in anything from milk tankers and brewing vessels to the kitchen sink. For example stainless steel can be rolled and formed into sheets with its smooth surface finish making it hygienic and easy to keep clean, and therefore ideal for use within the food processing industry, particularly in commercial kitchens.
In addition, due to their tolerance to aggressive conditions super austenitic grades are used in fermentation vessels where food stuff high in amino acids and salts need to be kept for a long period of time. Duplex steels, which have a have chromium levels of at least 22% are used for the more corrosive applications like mustard and vinegar production, canneries or dairies making cheeses.
Nearly 100 years after its discovery in Sheffield, the inert and non-toxic nature allied to stainless steels corrosion resistant properties make it the ideal material for the production of all food processing equipment, and within the food processing sector today stainless steel generally accounts for over 25% of the overall market. Much like William Rowland Limited which continues to thrive as a long-established metals and alloy supply company, Brearley's chrome steel has formed the basis for the wide range of stainless and special steels which are used throughout the world today.
