wash ware made of metal
Status: March 2007
Published by: Arbeitsgemeinschaft Gewerbliches Geschirrspülen
[Commercial Dishwashing Association]
Feithstraße 86, D-58095 Hagen, Germany
phone: +49 (0)2331/ 377 544 – 0
fax: +49 (0)2331/ 377 544 – 4
e-mail: mailto:[email protected]
The market for metal wash ware and for its cleaning and maintenance in the commercial sector
is characterized by huge variety in terms of materials and quality.
Statements regarding warewasher-safety may, because of the growing proliferation of
commercial warewashers, be of critical importance to the purchasing decision of the user. They
are an important parameter to use and should be queried with the manufacturer.
Cleaning in commercial warewashers can be assumed to place less of a load on wash ware
than automated warewashing in domestic warewashers.
For this reason, information from the manufacturer on suitability for domestic use can as a rule
also be applied to the warewashing process in the commercial sector.
What materials are used?
1. Non-cutting cutlery
1.1 Cutlery made of stainless steel
Stainless steel is the name used to designate steels
which are alloyed with 12% or more chromium and
may also contain nickel, molybdenum and other
metals. Products made from such steels are usually
labelled with a trademark.
The proportions of the individual constituents can affect the degree of corrosion resistance, which can in turn also lead to changes in other properties such as suitability for thermal hardening or magnetic properties.
Among the stainless steels, a distinction is made between chromium steel, chromium-nickel steel and chromium-nickel-molybdenum steel.
The various grades are identified under EN by their material numbers, e.g. 1.4301. Further information can be found in the VGG technical information sheet Commercial dishwashing & the resistance of materials in dishwashers
. A distinction should be made between cutlery made of non-magnetisable chromium-nickel steel containing approx. 18% chromium and approx. 9% nickel and cutlery made of magnetisable chromium steel containing approx. 13%-17% chromium.
Cutlery made of chromium-nickel steel is
Cutlery made of stainless chromium steel with a
chromium content of approx. 13%, on the other
hand, can not as a general rule
be assumed to
For warewashers with automated cutlery
removal, for which only stainless magnetisable steels are suitable, it is recommended that 17% chromium steels be used.
1.2 Silver-plated cutlery
Within the definition of this information sheet, these are
However, care should be taken with such cutlery to
ensure that, on account of its differing properties, e.g.
surface hardness, it is not washed in direct contact with
chromium steel cutlery and chromium-nickel steel
cutlery. 2. Cutting cutlery - knife blades,
hollow-handled knives, monobloc knives
At present, chromium steels with elevated carbon
content, suitable to thermal hardening, are the
preferred materials used for knife blades and monobloc
knives. They can be distinguished from chromium-
nickel- steels by their magnetic properties.
In contrast to the hollow-handled knife, in which the handle and the knife blade are made of different materials (e.g. chromium steel with elevated carbon content for the knife blades, chromium-nickel steel for
the handle), the monobloc knife - handle and knife.
blade - is forged from one piece. This type of knives is
predominantly only being used for cutlery of low grade
quality. As a rule, they are processed from stainless
chromium steels which vary in carbon content (up to
0.40%. Therefore, a monobloc knife cannot generally
assumed to be warewasher-proof.
If the handle is not thermally hardened, it can not
assumed to be warewasher-safe. Chromium and
chromium-molybdenum steels, suitable to thermal
hardening with a chromium content of more than 15%
are particularly suitable for cleaning in commercial
warewashers (see item 1.1).
When purchasing monobloc knives, it is recommended
ensuring that both the handle and the knife blade are
thermally hardened. 3. Stainless steel kitchenware and tableware
Due to its smooth non-porous surface and excellent
performance characteristics in terms of abrasion-
resistance, scratch-resistance, corrosion-resistance
and impact-resistance, stainless steel is also used for
pans, platters, containers and the like. In the main,
chromium-nickel steel is used here. Simple equipment
can also be manufactured from chromium steel.
With regard to resistance, the same statements apply
here as to cutlery.
Since stainless steel has low thermal conduction
properties, in general a so called sandwich layer is
applied to the pan base. This layer, which usually
consists of aluminium alloys, is not resistant to caustic
detergents and should therefore be fully encapsulated
by stainless steel. 4. Wash ware made of combinations of materials
With regard to wash ware made in material
combinations e.g. in wood, ceramic, non-ferrous metal
and plastic combinations, a general statement
concerning warewasher-resistance cannot be given.
The resistance is principally determined by the
materials that are used.
For example, where copper is used, discolourations
are frequently produced by the alkaline detergents
used. 5. Wash ware made of aluminium and non-ferrous
metals (e.g. copper, brass, zinc)
Equipment made of aluminium and non-ferrous metals
should no longer be used due to their low chemical
resistance and on hygiene grounds.
What influence does processing
Apart from the choice of materials in use, processing is
quality have on usability?
the key factor determining the warewasher-resistance of cutlery. It can basically be stated that the better the surface processing of cutlery is executed, the more warewasher-safe the cutlery will be. This is true not only to the main areas of front and backside but to a substancial degree also to minor areas such as e.g. the areas between the prongs of a fork. Here, only flawless processing will ensure that corrosion is prevented from occurring during commercial warewashing. The surface processing requirements are all the higher, the lower the grade of the material per se. This means, for example, that cutlery made from 17% chromium steels, as recommended for automated cutlery removal, should have better surface processing than cutlery made from chromium-nickel steels. In the case of knife blades and possibly also monobloc knives, the requirement for optimum possible surface processing is supplemented by the added requirements that the heat treatment of this material has been performed optimally and also that the pre-treatment stages in surface processing have been carried out such that no prior damage to the material has occurred. Appropriate tests are available for monitoring these properties, and these tests are regularly applied by prestigious manufacturers of high-quality cutlery. This provides a guarantee that, where such high-quality cutlery is used, no problems will occur if they are cleaned in commercial warewashers. As far as cutlery being positioned in the lower price segment is concerned, it cannot as a rule is assumed that this cutlery will be corrosion-resistant in every case.
The aforementioned remarks apply analogously to pots, pans and platters. In particular, joints between container and handle are often weak points in the processing and are thus more sharply exposed to corrosion attack.
Does stainless steel rust if used
The material is corrosion-resistant and permanently properly?
retains its shiny metallic appearance. Since no
protective layers have been applied, abrasion,
scratches, shocks or impacts do not detrimentally alter
its performance characteristics.
The usual cleaning, rinsing and water softening
processes, hot water or the final drying cycle do no
damage to higher-grade stainless steels.
If spots of rust do occur, then these will be
predominantly extraneous rust.
This may originate from rust particles carried along in
potable water or from washing together with non-
rustproof washware or from rusting dish racks being
Using or washing with metal pan scourers and such
like can also lead to the rusting of stainless steel items.
Where small rust spots have already appeared on
stainless steel, such spots should be removed
immediately. It usually suffices simply to rub them off,
but sometimes a non-scouring detergent is required.
Evenly spread corrosion, where the stainless steel is
ablated evenly from the surface, does in general not
occur. Nowadays, professionally processed stainless
steels are used which are of a quality that makes them
wholly suitable for automated dishwashing (see VGG
technical information sheet Commercial dishwashing &
resistance of materials in dishwashers
Pitting corrosion is a particular form of corrosion. Pitting corrosion
is the result of an excessively high
chloride load. Pitting corrosion involves the formation of
a rust-coloured spot, at the centre of which a small
crater develops. If this is not removed and, above all, if
the cause of the pitting corrosion is not eliminated, a
hole can develop in a relatively short space of time.
Pitting corrosion can be triggered by:
unsuitable steel alloys incorrect processing of the steel, defective
unsuitable water containing high chloride levels
together with dissolved cooking salt from food residues
prolonged action of acid and/or salt-containing
Malfunction of the water-softening equipment
What types of residues are there
It should categorically be stated that it is of crucial on wash ware and how can they
importance that no residues should remain on wash be prevented?
If deposits do occur, then these will, in particular, be
food residues that were not removed
Even assuming that the technical warewashing conditions (e.g. machine, agents, dosing, and handling) are fully complied with, poor warewashing results can still arise if food residues are allowed to dry on over a prolonged period, especially where heated trolleys are used, and inadequate pre-soaking is carried out. Unfavourable wash conditions can result in food residues which have already been removed being finely distributed and re-deposited on wash ware, including on items on which the food residues were not originally to be found. This occurs particularly where the detergent solution is too heavily loaded with food residues or the detergent dosage is too low.
lime deposits and other residues.
Water hardness levels that are too high, detergent dosages that are too low, water treatment equipment failures, combined waste-water hardness levels that are too high, or possibly a combination of several of the aforementioned factors can result in lime deposits.
Such deposits can be removed again by applying acidic products such as descaling agents. Detergent solution and food residues may remain on wash ware if the fresh water rinse is inadequate or wash ware is routinely too tightly arranged in the racks. Too high a mineral content in the water can also result in residues (spot formation). These can be prevented e.g. with the aid of a demineralisation unit (see VGG technical information sheet Commercial dishwashing & water
The prevention or removal of all the residues on stainless steel cutlery and wash ware listed here is vitally important, as full corrosion-proofing is provided only if, by virtue of unrestricted oxygen access, a wafer-thin, invisibly protecting passive layer can repeatedly re-form on the clean surface.
How are discolourations
Blue, violet or rainbow-like discolorations of the surface
of stainless steel are completely harmless but are perceived as being unattractive. They may be produced simply by water and contact with food. For example, discolorations of this kind can occur when cooking celeriac in stainless steel pans. Practical experience reveals that discolorations can be countered by an adequately high detergent dosage.
How can such discolorations be
The majority of discolorations can be removed again
with a suitable descaling solution (HCl-free), especially if this is done immediately after they appear. Some, however, can be removed again only by specialists (steel manufacturers, suppliers of agents). This is particularly true where they are allowed to "age" over a prolonged period, since they also become "fixed" as a result. Special cutlery soaking agents can also be used for removing such discolorations.
What has to be borne in mind
The basic rule for trouble-free use of a commercial when cleaning cutlery?
warewasher is to follow the instructions of the
It is equally important to take precise note of dosage
specifications and information on procedures from
agent manufacturers. Detergents in powder form must
not be sprinkled over cutlery as this can produce
persistant dark stains. Particular attention should be
paid to ensuring that the water treatment equipment is
functioning properly. The formation of problem-causing
deposits can in this way be prevented (see VGG
technical information sheets Commercial dishwashing
and Commercial dishwashing & water
The user must also take care to ensure that cutlery is
not inserted in special cutlery racks too closely together
immediately after it has been used.
Soaking cutlery in a heatable pre-soaking tank to which
a special soaking agent has been added (the relevant
instructions for use from the agent manufacturers
should be observed) so that the food residues cannot
dry on has been shown to be effective.
Pre-soaking cutlery and dishes with inappropriate high-
foaming manual washing-up liquids should always be
In addition, there are special machines for cleaning
cutlery which also permit the use of other methods.
What has to be borne in mind
Care should be taken to ensure that the wash ware is when purchasing stainless steel
designated “warewasher-safe” by the manufacturer. kitchenware and tableware?
The items should be as smooth as possible and have an easy-to-clean surface finish.
Technical advice provided by the
This technical information sheet, which has been member companies of the VGG
drawn up by experienced practitioners, is intended to draw the attention of the reader to the fact that commercial automated warewashing cannot be carried out successfully if it is approached superficially and without the appropriate involvement of all those participating in the warewashing process. Only an understanding of the technical processes and of the interdependencies that these entail, teamwork on the part of all those involved, in particular the operator of the warewasher and his/her personnel, and regular maintenance of the warewasher, dosing equipment and water treatment system by the manufacturer will produce the washing results expected by the user.
Consistent cooperation between warewasher, agent
and dosing equipment manufacturers as well as
manufacturers of water treatment equipment and wash
ware will ensure constant and optimum adaptation to
practical requirements, to the benefit of the customers
they share and of the environment.
Enquiries regarding this technical information sheet
“Commercial dishwashing & wash ware made of metal”
should be addressed to
Arbeitsgemeinschaft Gewerbliches Geschirrspülen,
Feithstraße 86, D-58095 Hagen, Germany
Phone: +49 (0)2331/ 377 544 – 0, Fax: +49 (0)2331/ 377 544 – 4, E-mail: [email protected]
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