The attractive and hygienic surface appearance of stainless steel products cannot be regarded as completely maintenance free. All grades and finishes of stainless steel may in fact stain, discolour or attain an adhering layer of grime in normal service. To achieve maximum corrosion resistance the surface of the stainless steel must be kept clean. Provided the grade, condition and surface finish were correctly selected for the particular service environment, fabrication and installation procedures were correct and that cleaning schedules are carried out regularly, good performance and long life will be achieved.
The iron in stainless steel is prevented from oxidizing by additives in the metal such as
Chromium in various concentrations depending on the grade. The chromium works by
reacting with oxygen to form a tough, adherent, passive layer of chromium oxide film
on the stainless steel surface. If minor chemical or mechanical damage occurs to the
surface, this film is usually self healing as long as it has enough oxygen. Because
oxygen is necessary for the reaction, liquids and other foodstuffs standing or stored for
a prolonged time on stainless can prevent oxygen contact and thus promote corrosion,
as can prolonged contact with cleaners such as bleach. Surface contamination and the
formation of deposits are also critical factors which may lead to drastically reduced life.
These contaminants may be minute particles of iron or rust or the result of other
chemical build ups. Industrial, commercial and even domestic and naturally occurring
atmospheric conditions can result in deposits which can be quite corrosive. Iron coming
in contact with the surface such as from metal cans or cast iron cooking equipment can
also promote corrosion and the formation of pitting.
Modern processes use many different cleaners, sterilizers and bleaches for hygienic
purposes. Cleaners for Stainless Steel must be appropriate for the application and used
in accordance with the manufacturers instructions. When used incorrectly (e.g. warm or
concentrated) even these products can cause discolouration and corrosion on the
surface of stainless steels.
Stainless steel exhibits good resistance to attack by many of the environments
encountered in domestic and commercial kitchen applications, however the resistance is
not ’iron clad’. Under certain specific conditions, especially involving chlorides and
exacerbated by elevated temperatures, small pits can form on the surface of steel.
These pits may continue to grow while the majority of the surface may still be
unaffected. To alleviate such growth, proper cleaning should take place as soon as
noticed on the surface. Crevice corrosion is where contaminant such as food is able to
penetrate a very narrow entry and become stagnant. Crevice corrosion usually occurs in
gaps a few micrometers wide only and can be induced by objects left standing on the
stainless steel surface.
Any corrosion stains on stainless steel should not be allowed to remain. They must be
thoroughly cleaned and dried as soon as possible.
Prep stations and other horizontal stainless steel surfaces are especially susceptible to
corrosion. Effort should be made to avoid trapped and pooled liquids on counter tops.
Clean up any food liquids and especially fruit and vegetable juices immediately following
preparation as well as any moisture remaining from the cleaning process.
Severe surface staining where moisture was trapped under a board left on a stainless
steel surface without very regular cleaning and drying.
Items such as cutting boards and bottles when left standing on stainless steel surfaces
can cause staining and crevice corrosion. It is imperative that items such as cutting
boards standing on a stainless steel surface are:
(This aids drying as well as ensuring that oxygen can come in contact with the metal
surface.)
Ensure surfaces are completely dry before replacing items for use.
Special consideration must be given to cleaning surfaces that may come into direct
contact with food during preparation and storage. Ensure that all cleaning processes
comply with regulations regards food safe compliance. Always wash down with soap or
a mild detergent and warm water followed by a clean water rinse.
Note: Some commercial Stainless Steel cleaners and ’Swipes’ leave a residue or film on
the metal, which may entrap fine particles of food thus deeming it not food-safe.
Always ensure that such products, and their application and use, comply with food
regulation requirements.
Advice is often sought concerning the frequency of cleaning of products made of stainless steel, and the answer is quite simply “clean the metal when it is dirty in order to restore its original appearance”. This may vary from once to four times a year for external applications or it may be once a day or more for an item in hygienic or aggressive situations. In many applications the cleaning frequency is after each use.
Stainless steel is easy to clean. Washing with soap or a mild detergent and warm water
followed by a clean water rinse is usually quite adequate for domestic and commercial
equipment. An enhanced appearance will be achieved if the cleaned surface is finally
wiped dry. Ideally, the surfaces should be thoroughly cleaned daily, with warm (not hot)
water and very mild cleaner and rinsing with clean water and where possible wiped dry
in the direction of the grain. Ensuring that all crevices and folds are wiped clean and
dry.
Remove any items such as cutting boards or bottles standing on the counter top
Cosmetic surfaces – non food contact. A weekly wipe over in the direction of the grain
with a rag impregnated with a light oil will enhance the stainless steel surface. Do not
over oil the surface, if necessary wipe down with a dry rag in the direction of the grain.