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Auto Dish & Glass Washing Introduction
1. Introduction
2. Machine Types
3. Temperature & Water Conditions
4. Top 10 Best Practises
5. Chemicals & Dosing
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1. Introduction
The first reliable hand-powered dishwasher was invented in 1887 by Josephine
Cochrane (US) and unveiled at the 1893 Chicago World’s Fair.
The Cochrane’s had a busy social life, and in 1870 when they moved into a large home,
ideal for entertaining, they regularly entertained guests using heirloom fine china.
After one event, when servants carelessly chipped some delicate dishes whilst washing
up, Mrs. Cochrane was furious and refused to allow the servants to handle the china
again.
The result was that, after every subsequent dinner party, she begrudgingly endured
dishpan hands wondering why someone had not invented a machine that could clean
dirty dishes, when machines had already been invented to sew clothes and cut grass.
Consumed by the challenge of inventing an automatic dish washer, she developed the
idea of securing the dishes in a rack whilst applying high pressure water to clean them.
Her husband William Cochran, who was a rising star in the Democratic Party, died in
1883 leaving a significant amount of debt, so the development of the dishwasher
escalated from a project of convenience to a project for survival. Her first creation had
wire compartments for plates, cups and saucers which were put inside a wheel that
lay flat inside a copper boiler. A motor turned the wheel, pumping hot soapy water
from the bottom of the boiler over the dishes, but it didn’t really work too well, so she
got help with the design from mechanic George Butters, and the first patent on the
refined design of the Garis-Cochran Dish-Washing Machine was issued on 28th
December, 1886.
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It was much later, in 1924, when William Howard Livens (UK) invented a small
dishwasher that was actually suitable for domestic use. This was the first modern
dishwasher, and incorporated most of the design elements that feature in the models
of today – a front door for loading, a wire rack to hold the dirty crockery and a rotating
sprayer. Drying elements were added to his design in 1940. It was the first machine
suitable for domestic use, and it came at a time when permanent plumbing and
running water was becoming increasingly common in residential properties.
Although there have been many improvements in design and components over the
years, the basic functions of a dishwasher are essentially the same as before. A dish or
glass washer is simply a machine designed to clean and disinfect plates, cups, glasses,
cutlery, utensils, and trays by spraying a detergent solution to clean and a rinse
additive to aid drying. By rinsing at high temperature (71*C for 7 seconds), items are
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also disinfected, so a commercial ware washing machine is now a time-saving necessity
and valued capital asset for any commercial food and beverage operation.
Although large commercial dish washers look daunting and complex, they can be
regarded simply as large stainless steel boxes that can wash and rinse items in water
that is hotter than can be used safely by hand.
When a dish washing machine is first switched on, a solenoid valve (an electrically
operated tap) is opened to allow fresh mains water to flow into the “Wash Tank”
where electric elements heat the water to between 55ºC – 65ºC. As the wash tank is
filling, an initial charge (amount) of chemical detergent is dosed at the appropriate
level. We will look at the subject of chemical dosing in a later post within this series.
The initial charge is the amount of detergent that is added to the water in the wash
tank to achieve a detergent concentration that will clean effectively at optimum levels.
The detergent is dosed by a small electric pump and the amount dosed is programmed
depending on the site water conditions and other factors (see later post on the impacts
of hard water and lime-scale on wash performance). Once the correct amount of water
and detergent is in the tank, and the rack of soiled dishes has been placed into the
machine, the washing process begins.
In the wash process, the hot detergent/water solution is pumped from the wash tank
through washing arms, fitted with spray nozzles, mounted above and below the racks
of dishes. The pressure of the water jets causes the wash arms to rotate and disperse
the spray on to the items being cleaned. In a well-maintained machine, the pressure
of the spray is high and the mechanical action of the water striking the soiled surfaces,
combined with the chemical action from the detergent, allows effective cleaning. The
soiling is either completely emulsified by the hot detergent solution or flushed from
the surfaces to be collected on scrap trays situated within the machine for later
removal.
When the washing stage is complete, the items in the dishwasher are rinsed with clean,
hot water. During the rinse cycle a specialised chemical called a rinse aid is dosed into
a small boiler in the dishwasher that heats the water to 820C – 880C and the hot
solution is sprayed onto the items in the racks to flush away any detergent residues
and to assist streak free drying.
The chemical rinse aid simply speeds up the drying of the items by allowing the hot
water to be shed from the surface efficiently without runs or water marks. In later
posts we will examine the importance of consistent temperatures and the removal of
lime scale in achieving maximum cleaning results.
Acknowledgements:
http://forgottennewsmakers.com/2010/04/20/josephinecochrane-1839-1913-
invented-the-dishwasher/
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2. Machine Types
Following the brief overview of the origins and history of the dishwasher presented in
Part 1, this post describes the most common types of dish and glass washer machines
available to commercial food and beverage operations. We have posted some machine
manufacturer links at the end of the post.
It is important to note that although machinery and chemical companies are closely
linked, they invariably don’t work closely enough together. Problems with wash results
are routinely directed towards the chemical supplier in the first instance because, in
most cases, they will visit the site free of charge, whereas the machinery company will
routinely charge for the visit. R.P. Adam collaborates with all machinery suppliers to
work in the best interests of their mutual clients.
New dish and glass washers can range from £1,000 to £25,000+ so with this significant
capital outlay it makes sense to have a preventative maintenance programme set up
from the outset. Pumps need maintained, peristaltic tubes need changed and heating
elements will degrade and fail over time. Likewise, essential parts such as wash jets,
rinse jets and door seals should be maintained and replaced as required.
Commercial Under-Counter Dish & Glass Washers (Front Loaders)
Also referred to as a front loader type machines, these are perfect for the licensed
trade, small retail catering outlets where space restrictions apply and are commonly
used on hospital wards. They are built to accommodate different interchangeable
plastic racks which come in various sizes and capacities. The relative performance of
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the machine models is normally measured by the number of plates or pint glasses
washed per hour.
Hood Type Dish Washers
The single tank, single cycle pass-through dish washer is one of the most common
machine types used today. They are usually configured as a straight through or corner
style model and fitted with custom stainless steel tabling for sliding the dishwashing
racks directly into and out of the machine.
They use different interchangeable plastic racks and the capacity of the machine is
measured by the number of plates washed per hour. There is often a sink and
overhead pre-spray system fitted alongside these machines to pre-spray loose food
debris prior to entry into the machine.
Conveyor Type Dish Washers (Rack Conveyors)
Also referred to as rack conveyors, they are designed to “pull” the wash racks through
the wash cycle on a chain conveyor. Usually found in larger catering departments such
as university refectories, large cafeterias and hospital main catering departments
serving between 250 to 1500 meals during peak hours per day. Although the washing
capacity depends upon the length of the machine, they usually wash up to 400 racks
per hour.
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Flight Type Dish Washers
Also referred to as “rack-less”, “belt conveyor” or “tunnel” machines, they do not use
wash racks because the wash items are placed directly onto the conveyor belt. Most
flight type dish washers are individually designed and custom-built for the
requirements of each operation and are commonly found in mass catering/banqueting
areas, airline catering operations and large hospital main catering departments. The
largest machines are capable of washing tens of thousands of dishes per hour.
Pot & Pan Washers
Pot and pan washers utilise much higher water pressure and longer wash cycle times
to remove baked-on food from large pots, pans, baking sheets and food preparation
vessels. These are found in food processing factories like commercial bakeries and
airline catering operations where there is a requirement for industrial scale cleaning
of larger heavily soiled items.
Although not an exhaustive list the following machine manufacturers’ provide good
quality equipment for all types of operations:
• Hobart (http://www.hobartuk.com/warewashing)
• Meiko (http://www.meiko-uk.co.uk/products/warewashing/)
• Winterhalter (http://www.winterhalter.co.uk/)
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3. Temperature & Water Conditions
In this post we look at two critical factors that affect wash performance in any dish or
glass washer operation – maintaining correct wash and rinse temperatures and
knowing the hardness of the water coming into the machine.
Maintaining the correct temperatures is critical in achieving clean dishes or glasses.
• Optimum WASH temperature: Failure to achieve the correct wash temperature
will lead to poor cleaning performance, poor removal of protein residues and
possible foaming on an industrial scale!
• Optimum RINSE temperature: Failure to maintain the correct rinse temperature
will result in wet crockery and cutlery, streaking and spotting.
For Commercial Dish Washers:
• Pre-Wash Tank: 50-55°C
• Main-Wash Tank: 60-65°C
• Rinse Boiler Tank: 82-88°C
• Final Rinse: 88-90°C
For Commercial Glass Washers:
• Main-Wash Tank: 50-60°C
• Rinse Boiler Tank: 82-88°C
It is critical that these temperature thresholds are adhered to. A reputable chemical
company offering regular field service visits will record the wash and rinse
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temperatures and notify the customer if the temperatures are incorrect. The chemical
supplier has no authority to tamper with the dish washer itself, so it is important that
the machine manufacturer is contacted to rectify below par temperature settings and
delivery.
Operators should be aware that every item that enters into a dish or glass washer is
colder than the wash water in the tank, therefore the temperature of the wash water
will drop slightly after each cycle. If the machine is used continuously without a
recovery period to allow the water to be re-heated, cleaning performance is likely to
become progressively worse.
Note: Some machines have dedicated wash programmes (like laundry machines) that
wash at either lower or higher temperatures than those stated above because of
specific requirements – for example, there may be a dedicated washing programme
for polycarbonate glass.
Combatting the Effects of Lime-Scale
If you live in a hard water area (please see the hard water maps of the UK and UAE
below) and look inside your kettle, you will notice a tough, stony, off-white crust inside,
particularly surrounding the heating element. This is lime-scale, a mineral deposit left
behind when hard water is heated or boiled.
Rainwater is naturally ‘soft’, containing few impurities and if it runs over/through less
permeable rocks like granite or slate, it remains as such. However if rain water runs
through soft, spongy rocks, like lime stone or chalk, it absorbs minerals from them.
These dissolved minerals, often calcium or magnesium carbonate, are what makes the
water “hard”. Where acid rain precipitates, especially over metropolitan and industrial
areas, this process is speeded up considerably.
Quite simply it is more difficult to wash in hard water. If you have tried to use soap or
shampoo in central London, for example, you may have noticed that the soap does not
lather readily and you may have to use more to get the desired effect. In the same
way, if the chemicals used are not the right formulations for the water quality, they
will be less effective and more will be required.
Some of the minerals found in hard water possess a chemical property called “inverse
solubility”, meaning that they dissolve more easily in cold water than in hot. So as the
temperature increases, the dissolved salts start toun-dissolve and deposit on surfaces.
This is why you normally see the heaviest deposits around the heating element, the
hottest part, in a domestic kettle (or dish washer).
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In commercial dish and glass washing, a bigger problem arises if the untreated hard
water is heated above 55°C or left to stand. The dissolved minerals within the water
will dry out and solidify onto wash jets and metals surfaces as the water evaporates.
This solidified mineral coating is lime-scale and is the cause of many problems in both
domestic and commercial premises.
On an industrial level, the presence of lime-scale makes the machines less
energyefficient. According to British Water, a 1.6mm coating of lime scale on a heating
element can make it up to 12% less effective.
Imagine the impact on a multiple-chain of restaurants, hotels or bars, whose estate is
primarily located in hard water areas, incurring a 12% increase in energy costs because
of poor machine maintenance/failure to combat lime-scale?
Softening Water Reduces the Negative Impacts of Lime-Scale
Water softening is the most common method of treating hard water. It works by a
fairly simple chemical process – swapping the calcium which forms lime-scale for
sodium, which is more likely to stay dissolved. In simple terms this is how a commercial
water softener works:
1. As water enters the system it passes through an ion exchange column filled with
thousands of tiny beads of resin.
2. This resin has charged sodium attached to its surface and it swaps this for the
more reactive calcium and magnesium as water flows over it.
3. The resin can continue to do this indefinitely as long as it is washed through with
salt water every so often to wash off the calcium and magnesium and replace
the sodium. Most modern columns will automatically rinse themselves if
regularly provided with salt.
Most dish washers have either a built-in softener or a separate water softening
dispenser which removes hardness from water and prevents the formation of a white
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film on glassware or crockery. It is vital that staff are aware of the importance of this
piece of equipment and know how to replenish the softener.
To find out whether your business premises are in a hard water area, please see the
maps below:
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If there is a lime-scale build-up within your dish or glass washer, this can be removed
by using an acidic liquid descaler as follows:
(http://www.rpadam.co.uk/products/product-items/descaler-2x5lt/)
1. Switch off the electronic wall mounted dosing equipment (if applicable).
2. Dilute the descaler with up to 20 parts water depending on the degree of scale
build up and add directly into the wash tank.
3. For best results, heat up the water to working temperature and circulate until
all scale is removed.
4. Drain solution, refill and rinse thoroughly with clean water.
5. Drain again and refill with clean water.
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4. Top 10 Best Practises
Many of the negative impacts affecting dish and glass washing results can easily be
overcome by adhering to some very basic rules like thorough pre-scrapping, prerinsing
(above photo) and effective racking and stacking. Here are some key issues to address:
1. Scrape all food debris from plates and ensure all heavily soiled items are
prerinsed prior to entering the machine. Always remove solid debris like cocktail
sticks, fruit peel, pips, paper etc. from glasses and plates. They can block the
wash jets and impair performance.
2. Rack items of the same size together so none are hidden from wash jets. Fill the
racks evenly but not too tightly making sure items are well-spaced so that the
wash solution gets an even coverage.
3. When loading glassware always ensure that the baskets are filled to capacity to
minimise breakages and place cups and glasses upside down to allow the wash
water to spray in from below. Always stand glasses on drip mats to dry.
4. Allow crockery to air dry – never use a tea towel as it can harbour bacteria and
may contaminate the items which have already been thermally disinfected.
5. Always mix different types of cutlery in baskets to avoid items sticking together
and ensure that they are stacked in baskets with the handles down – eating end
up.
6. All pots and pans and larger utensils should be washed by hand unless there is
a dedicated pan washer for larger items.
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7. Remember to “dump” the wash water after each session and refill with fresh
water, otherwise the machine will be re-circulating dirty water.
8. Ensure that the filter trays within the machine are checked and cleaned so that
larger items of debris do not re-circulate and impede the wash performance.
9. Ensure that the machine wash and rinse jets are cleaned on a weekly basis and
are free of food debris, broken glass and lime-scale. If these jets are blocked the
wash water will not make effective contact with the items to be washed.
10. In hard water areas where lime-scale is a problem, ensure that the machine is
descaled once a week with a liquid phosphoric acid descaler. Lime-scale build
up will significantly reduce the efficiency of the machine and will consume far
more energy than normally required.
The dish and glass washer needs cleaned like any other piece of catering equipment or
surface, so ensure you clean thoroughly the inside of the machine after each session:
1. Shut off machine at the mains supply and not just on the machine.
2. Open the drain plugs to empty the machine completely.
3. Remove the curtains and clean with a degreaser/sanitiser.
4. Remove both wash and rinse arms and clean out all debris.
5. Remove scrap trays and clean out all debris.
6. Thoroughly clean out the inside of the machine with a degreaser/sanitiser and
rinse thoroughly.
7. Replace scrap trays, wash and rinse arms and curtains.
8. Shut doors and switch on and allow machine to heat up to correct working
temperature.
9. Machine is now ready to operate.
10. Ensure no broken parts (like missing wash & rinse jets for example).
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5. Chemicals & Dosing
In this post we look at chemicals and chemical dosing. For best results, commercial
dish washers are normally fitted with electronic dosing pumps to dispense the
chemicals. Electronic chemical dosing pumps are programmed to allow dish washer
detergent and rinse additive to be metered precisely and consistently into the correct
wash cycle.
There are two methods of pumping detergent and rinse aid into a dish or glass washer:
1. Via pumps located within the design of the washing machine itself – this is called
“integral feed” and these are usually found on smaller capacity machines like
cabinet glass washers. The pumps are pre-set by the machine manufacturer to
try to accommodate most liquid chemicals available on the market. This often
means that the pumps dose more chemical than required for optimum cleaning.
The chemical manufacturer therefore only supplies the chemical and has no real
input into dose levels.
2. Via external dosing pumps which are usually provided Free-On-Loan by a
reputable chemical manufacturer who will fit the dosing unit and set the dose
rates for their specific chemicals and tailored to site requirements.
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There are different types of electronic dosing systems available but most chemical
suppliers use timed (or cyclic) dosing to get their products into the wash tanks in a
controlled manner. Calculated chemical dose levels are pre-set by the chemical
manufacturer to ensure the optimum concentration of chemical is used in each wash
cycle, taking into account the amount of water in the wash tank and the volume of
water added in the rinse cycle. The pumps are then calibrated and dose levels are
programmed into the memory of the dosing unit to ensure that the correct amount of
chemical detergent and rinse aid is added every time.
In future posts we will examine the pros and cons of timed dosing versus probe based
dosing. In simple terms this type of dosing is based on the premise that a probe
(located in the wash tank) detects the concentration of chemical available. If the
concentration is too low, it “asks for more” and the pumps dose additional detergent
to the required level. If the probe’s detection sensitivity is compromised (by being
scaled up or enveloped in debris) it will falsely ask for more detergent when it is not
required, meaning the machine asks for more than is required.
Although not an exhaustive list the following dosing unit manufacturers provide good
quality equipment for all types of operations:
• Brightwell Dispensers (http://www.brightwell.co.uk/dishwash)
• Dema (http://www.demaeng.com/kitchen-food-
service/warewashingdishwashing/)
• Knight (http://www.knightequip.com/kitchen.html)
• Seko (http://www.sekousa.com/category.php?c=Warewashing)
It is also worth considering setting up a preventative maintenance schedule with your
chemical supplier, who will check, service and maintain chemical dosing units on a
regular basis. A reputable chemical manufacturer will have an experienced team of
service personnel who will routinely change pump heads and peristaltic tubing to
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ensure consistent dosing and will have access to qualified electrical engineers to fit
and repair sophisticated dosing equipment.
The supplier should regularly conduct titration tests of the wash tank solution to
ensure the correct chemical concentration levels are being maintained. They should
also conduct temperature tests so that clients have hygienically clean and dry
crockery, cutlery and glassware.
Wasted time is wasted money; therefore a prompt, reliable, efficient and professional
engineering function from your chemical supplier is essential to maintain the
operational efficiency of a commercial dishwashing operation. Customers need to
know that if a breakdown is reported it is dealt with in a prompt and efficient manner
to ensure as little downtime as possible for the operator.
For further information on the types of chemicals available for automatic dish and glass
washing click here (http://www.rpadam.co.uk/products/dish-glass-washing/)
Both RP Adam and Arpal Gulf (following the completion of a new account installation)
operate systems whereby a schedule of on-going service calls is automatically
generated, thus offering customers unrivalled engineering support. Our technicians’
vehicles are well stocked with a wide variety of equipment, spares and tools, ensuring
that work can be completed at the first visit. Our objective is always the same –
complete the work first time, every time.
It should be noted that the automatic dish, glass and pot wash detergents that are
automatically dosed into machines are almost all corrosive to the eyes and skin, so
great care should be taken when handling these types of products and the
appropriate eye and skin protection used.
As safety is our primary focus at all times, we will shortly be unveiling a brand new
“Ultra-Safe” liquid dish and glass washing system…watch this space.
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