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A dishwasher is a machine that is used to clean
dishware Tableware is any dish or dishware used for setting a table, serving food, and dining. It includes cutlery, glassware, serving dishes, and other items for practical as well as decorative purposes. The quality, nature, variety and number of ob ...
,
cookware Cookware and bakeware is food preparation equipment, such as cooking pots, pans, baking sheets etc. used in kitchens. Cookware is used on a stove or range cooktop, while bakeware is used in an oven. Some utensils are considered both cookware ...
, and
cutlery Cutlery (also referred to as silverware, flatware, or tableware), includes any hand implement used in preparing, serving, and especially eating food in Western culture. A person who makes or sells cutlery is called a cutler. The city of Sheffie ...
automatically. Unlike manual dishwashing, which relies heavily on physical scrubbing to remove soiling, the mechanical dishwasher cleans by spraying hot water, typically between , at the dishes, with lower temperatures of water used for delicate items. A mix of water and dishwasher detergent is pumped to one or more rotating sprayers, cleaning the dishes with the cleaning mixture. The mixture is recirculated to save water and energy. Often there is a pre-rinse, which may or may not include detergent, and the water is then drained. This is followed by the main wash with fresh water and detergent. Once the wash is finished, the water is drained; more hot water enters the tub by means of an electromechanical
solenoid valve A solenoid valve is an electromechanically operated valve. Solenoid valves differ in the characteristics of the electric current they use, the strength of the magnetic field they generate, the mechanism they use to regulate the fluid, and the ...
, and the rinse cycle(s) begin. After the rinse process finishes, the water is drained again and the dishes are dried using one of several drying methods. Typically a rinse-aid, a chemical to reduce the surface tension of the water, is used to reduce water spots from
hard water Hard water is water that has high mineral content (in contrast with "soft water"). Hard water is formed when water percolates through deposits of limestone, chalk or gypsum, which are largely made up of calcium and magnesium carbonates, ...
or other reasons. In addition to domestic units, industrial dishwashers are available for use in commercial establishments such as hotels and restaurants, where many dishes must be cleaned. Washing is conducted with temperatures of and sanitation is achieved by either the use of a booster heater that will provide an "final rinse" temperature or through the use of a chemical sanitizer.


History

The first mechanical dishwashing device was registered for a patent in 1850 in the United States by Joel Houghton. This device was made of wood and was cranked by hand while water sprayed onto the dishes. The device was both slow and unreliable. Another patent was granted to L.A. Alexander in 1865 that was similar to the first but featured a hand-cranked rack system. Neither device was practical or widely accepted. Some historians cite as an obstacle to adoption the historical attitude that valued women for the effort put into housework rather than the results—making household chores easier was perceived by some to reduce their value. The most successful of the hand-powered dishwashers was invented in 1886 by Josephine Cochrane together with mechanic George Butters in Cochrane's tool shed in
Shelbyville, Illinois Shelbyville is a city in and the county seat of Shelby County, Illinois, United States, along the Kaskaskia River. As of the 2020 census, the population was at 4,674. HSHS Good Shepherd Hospital, located in town, is the county's only hospital. S ...
when Cochrane (a wealthy socialite) wanted to protect her
china China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
while it was being washed. Her invention was unveiled at the 1893 World's Fair in
Chicago (''City in a Garden''); I Will , image_map = , map_caption = Interactive Map of Chicago , coordinates = , coordinates_footnotes = , subdivision_type = Country , subdivision_name ...
under the name of Lavadora but was changed to Lavaplatos as another machine invented in 1858 already held that name. Cochrane's inspiration was her frustration at the damage to her good china that occurred when her servants handled it during cleaning. Europe's first domestic dishwasher with an electric motor was invented and manufactured by
Miele Miele ( ; ) is a German manufacturer of high-end domestic appliances and commercial equipment, headquartered in Gütersloh, Ostwestfalen-Lippe. The company was founded in 1899 by Carl Miele and Reinhard Zinkann, and has always been a family- ...
in 1929. In the United Kingdom, William Howard Livens invented a small, non-electric dishwasher suitable for domestic use in 1924. It was the first dishwasher that incorporated most of the design elements that are featured in the models of today; it included a 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 in the home were becoming increasingly common. Despite this, Liven's design did not become a commercial success, and dishwashers were only successfully sold as domestic utilities in the postwar boom of the 1950s, albeit only to the wealthy. Initially, dishwashers were sold as standalone or portable devices, but with the development of the wall-to-wall
countertop A countertop, also counter top, counter, benchtop, worktop (British English) or kitchen bench (Australian or New Zealand English), bunker ( Scottish English) is a raised, firm, flat, and horizontal surface. They are built for work in kitchens or ...
and standardized height cabinets, dishwashers began to be marketed with standardized sizes and shapes, integrated underneath the kitchen countertop as a modular unit with other kitchen appliances. By the 1970s, dishwashers had become commonplace in domestic residences in North America and Western Europe. By 2012, over 75 percent of homes in the United States and Germany had dishwashers. In the late 1990s, manufacturers began offering various new
energy conservation Energy conservation is the effort to reduce wasteful energy consumption by using fewer energy services. This can be done by using energy more effectively (using less energy for continuous service) or changing one's behavior to use less service (f ...
features in dishwashers. One feature was use of "soil sensors", which was a computerized tool in the dishwasher which measured food particles coming from dishes. When the dishwasher had cleaned the dishes to the point of not releasing more food particles, the soil sensor would report the dishes as being clean. The sensor operated with another innovation of using variable washing time. If dishes were especially dirty, then the dishwasher would run for a longer time than if the sensor detected them to be clean. In this way, the dishwasher would save energy and water by only being in operation for as long as needed.


Design


Size and capacity

Dishwashers that are installed into standard kitchen cabinets have a standard width and depth of 60 cm (Europe) or (US), and most dishwashers must be installed into a hole a minimum of 86 cm (Europe) or (US) tall. Portable dishwashers exist in 45 and 60 cm (Europe) or (US) widths, with casters and attached countertops. There are also dishwashers available in sizes according to the European
gastronorm Gastronorm (GN), sometimes spelled ''Gastro-Norm'', is a European standard for kitchenware tray and container sizes that is commonly seen worldwide in the catering and professional food industry, as well as in certain parts of the high-end consum ...
standard. Dishwashers may come in standard or tall tub designs; standard tub dishwashers have a service kickplate beneath the dishwasher door that allows for simpler maintenance and installation, but tall tub dishwashers have approximately 20% more capacity and better sound dampening from having a continuous front door. The international standard for the capacity of a dishwasher is expressed as standard
place setting Table setting (laying a table) or place setting refers to the way to set a table with tableware—such as eating utensils and for serving and eating. The arrangement for a single diner is called a place setting. It is also the layout in which t ...
s. Commercial dishwashers are rated as plates per hour. The rating is based on standard-sized plates of the same size. The same can be said for commercial glass washers, as they are based on standard glasses, normally pint glasses.


Layout

Present-day machines feature a drop-down front panel door, allowing access to the interior, which usually contains two or sometimes three pull-out racks; racks can also be referred to as "baskets". In older U.S. models from the 1950s, the entire tub rolled out when the machine latch was opened, and loading as well as removing washable items was from the top, with the user reaching deep into the compartment for some items. Youngstown Kitchens, which manufactured entire kitchen cabinets and sinks, offered a tub-style dishwasher, which was coupled to a conventional kitchen sink as one unit. Most present-day machines allow for placement of dishes, silverware, tall items and cooking utensils in the lower rack, while glassware, cups and saucers are placed in the upper rack. One notable exception were dishwashers produced by the Maytag Corporation from the late sixties until the early nineties. These machines were designed for loading glassware, cups and saucers in the lower rack, while plates, silverware, and tall items were placed into the upper rack. This unique design allowed for a larger capacity and more flexibility in loading of dishes and pots and pans. Today, "dish drawer" models eliminate the inconvenience of the long reach that was necessary with older full-depth models. "Cutlery baskets" are also common. A
drawer dishwasher A dishdrawer is a type of dishwashing machine invented, designed and manufactured by Fisher & Paykel. They are available under several brands depending on geographic location Fisher & Paykel, Kenmore Appliances, KitchenAid, and Bauknecht followin ...
, first introduced by
Fisher & Paykel Fisher & Paykel Appliances Holdings Ltd () is a major appliance manufacturer which is a subsidiary of Chinese multinational home appliance manufacturer Haier. It is a multinational corporation based in East Tāmaki, New Zealand. Originally ...
in 1997, is a variant of the dishwasher in which the baskets slide out with the door in the same manner as a drawer
filing cabinet A filing cabinet (or sometimes file cabinet in American English) is a piece of office furniture for storing paper documents in file folders. In the most simple context, it is an enclosure for drawers in which items are stored. The two most com ...
, with each drawer in a double-drawer model being able to operate independently of the other. The inside of a dishwasher in the North American market is either
stainless steel Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's r ...
or
plastic Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptab ...
. Most of them are stainless steel body and plastic made racks. Stainless steel tubs resist
hard water Hard water is water that has high mineral content (in contrast with "soft water"). Hard water is formed when water percolates through deposits of limestone, chalk or gypsum, which are largely made up of calcium and magnesium carbonates, ...
, and preserve heat to dry dishes more quickly. They also come at a premium price. Dishwashers can be bought for as expensive as $1,500+, but countertop dishwashers are also available for under $300. Older models used baked enamel tubs, while some used a
vinyl Vinyl may refer to: Chemistry * Polyvinyl chloride (PVC), a particular vinyl polymer * Vinyl cation, a type of carbocation * Vinyl group, a broad class of organic molecules in chemistry * Vinyl polymer, a group of polymers derived from vinyl ...
coating bonded to a steel tub, which provided protection of the tub from acidic foods and provided some sound attenuation. European-made dishwashers feature a stainless steel interior as standard, even on low-end models. The same is true for a built-in
water softener Water softening is the removal of calcium, magnesium, and certain other metal cations in hard water. The resulting soft water requires less soap for the same cleaning effort, as soap is not wasted bonding with calcium ions. Soft water also ext ...
.


Washing elements

European dishwashers almost universally use two or three sprayers which are fed from the bottom and back wall of the dishwasher leaving both racks unimpeded and also such models tend to use inline water heaters, removing the need for exposed elements in the base of the machine that can melt plastic items near to them. Many North American dishwashers tend to use exposed elements in the base of the dishwasher. Some North American machines, primarily those designed by General Electric, use a wash tube, often called a wash-tower, to direct water from the bottom of the dishwasher to the top dish rack. Some dishwashers, including many models from
Whirlpool A whirlpool is a body of rotating water produced by opposing currents or a current running into an obstacle. Small whirlpools form when a bath or a sink is draining. More powerful ones formed in seas or oceans may be called maelstroms ( ). ''V ...
and
KitchenAid KitchenAid is an American home appliance brand owned by Whirlpool Corporation. The company was started in 1919 by The Hobart Manufacturing Company to produce stand mixers; the "H-5" was the first model introduced. The company faced competition ...
, use a tube attached to the top rack that connects to a water source at the back of the dishwasher and directs water to a second wash spray beneath the upper rack, this allows full use of the bottom rack. Late-model
Frigidaire Frigidaire Appliance Company is the American consumer and commercial home appliances brand subsidiary of multinational company Electrolux. Frigidaire was founded as the Guardian Frigerator Company in Fort Wayne, Indiana, and developed the firs ...
dishwashers shoot a jet of water from the top of the washer down into the upper wash sprayer, again allowing full use of the bottom rack (but requiring that a small funnel on the top rack be kept clear).


Features

Mid range to higher end North American dishwashers often come with hard food disposal units, which behave like miniature garbage (waste) disposal units that eliminate large pieces of
food waste Food loss and waste is food that is not eaten. The causes of food waste or loss are numerous and occur throughout the food system, during production, processing, distribution, retail and food service sales, and consumption. Overall, abou ...
from the wash water. One manufacturer that is known for omitting hard food disposals is Bosch, a German brand; however, Bosch does so in order to reduce noise. If the larger items of food waste are removed before placing in the dishwasher, pre-rinsing is not necessary even without integrated waste disposal units. Many new dishwashers feature
microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circ ...
-controlled,
sensor A sensor is a device that produces an output signal for the purpose of sensing a physical phenomenon. In the broadest definition, a sensor is a device, module, machine, or subsystem that detects events or changes in its environment and sends ...
-assisted wash cycles that adjust the wash duration to the number of dirty dishes (sensed by changes in water
temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...
) or the amount of dirt in the rinse water (sensed chemically or optically). This can save water and energy if the user runs a partial load. In such dishwashers the
electromechanical In engineering, electromechanics combines processes and procedures drawn from electrical engineering and mechanical engineering. Electromechanics focuses on the interaction of electrical and mechanical systems as a whole and how the two systems ...
rotary switch A rotary switch is a switch operated by rotation. These are often chosen when more than 2 positions are needed, such as a three-speed fan or a CB radio with multiple frequencies of reception or "channels". A rotary switch consists of a spindle ...
often used to control the washing cycle is replaced by a microprocessor, but most sensors and
valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fitting ...
s are still required. However, pressure switches (some dishwashers use a pressure switch and flow meter) are not required in most microprocessor controlled dishwashers as they use the motor and sometimes a rotational position sensor to sense the resistance of water; when it senses there is no
cavitation Cavitation is a phenomenon in which the static pressure of a liquid reduces to below the liquid's vapour pressure, leading to the formation of small vapor-filled cavities in the liquid. When subjected to higher pressure, these cavities, ca ...
it knows it has the optimal amount of water. A bimetal switch or wax motor opens the detergent door during the wash cycle. Some dishwashers include a child-lockout feature to prevent accidental starting or stopping of the wash cycle by children. A child lock can sometimes be included to prevent young children from opening the door during a wash cycle. This prevents accidents with hot water and strong detergents used during the wash cycle.


Process


Energy use and water temperatures

In the European Union, the energy consumption of a dishwasher for a standard usage is shown on a European Union energy label. In the United States, the energy consumption of a dishwasher is defined using the
energy factor An energy factor is a metric used in the United States to compare the energy conversion efficiency of residential appliances and equipment. The energy factor is currently used for rating the efficiency of water heaters, dishwashers, clothes washer ...
. Most consumer dishwashers use a 75 °C (167 °F) thermostat in the sanitizing process. During the final rinse cycle, the heating element and wash pump are turned on, and the cycle timer (electronic or electromechanical) is stopped until the thermostat is tripped. At this point, the cycle timer resumes and will generally trigger a drain cycle within a few timer increments. Most consumer dishwashers use 75 °C (167 °F) rather than 83 °C (181 °F) for reasons of burn risk, energy and water consumption, total cycle time, and possible damage to plastic items placed inside the dishwasher. With new advances in detergents, lower water temperatures (50–55 °C / 122–131 °F) are needed to prevent premature decay of the enzymes used to eat the grease and other build-ups on the dishes. In the US, residential dishwashers can be certified to a
NSF International NSF (an initialism for National Sanitation Foundation) is a product testing, inspection, certification organization with headquarters in Ann Arbor, Michigan. NSF also offers consulting and training services worldwide. History NSF Internatio ...
testing protocol which confirms the cleaning and sanitation performance of the unit.
Superheated steam Superheated steam is steam at a temperature higher than its vaporization point at the absolute pressure where the temperature is measured. Superheated steam can therefore cool (lose internal energy) by some amount, resulting in a lowering of its ...
dishwashers can kill 99% of bacteria on a plate in just 25 seconds.


Drying

The heat inside the dishwasher dries the contents after the final hot rinse. North American dishwashers tend to use heat-assisted drying via an exposed element which tends to be less efficient than other methods. European machines and some high end North American machines use passive methods for drying – a stainless steel interior helps this process and some models use heat exchange technology between the inner and outer skin of the machine to cool the walls of the interior and speed up drying. Some dishwashers employ desiccants such as
zeolite Zeolites are microporous, crystalline aluminosilicate materials commonly used as commercial adsorbents and catalysts. They mainly consist of silicon, aluminium, oxygen, and have the general formula ・y where is either a metal ion or H+. These p ...
which at the beginning of the wash are heated, dry out and creating steam which warms plates, and then are cooled during the dry cycle which absorbs moisture again, saving significant energy. Plastic and non-stick items form drops with smaller surface area and may not dry properly compared to china and glass, which also store more heat that better evaporate the little water that remains on them. Some dishwashers incorporate a fan to improve drying. Older dishwashers with a visible heating element (at the bottom of the wash cabinet, below the bottom basket) may use the heating element to improve drying; however, this uses more energy. Most importantly however, the final rinse adds a small amount of rinse-aid to the hot water, this is a mild detergent that improves drying significantly by reducing the inherent surface tension of the water so that water mostly drips off, greatly improving how well all items, including plastic items, dry. Most dishwashers feature a drying sensor and as such, a dish-washing cycle is always considered complete when a drying indicator, usually in the form of an illuminated "end" light, or in more modern models on a digital display or audible sound, exhibits to the operator that the washing and drying cycle is now over. US Governmental agencies often recommend air-drying dishes by either disabling or stopping the drying cycle to save energy.


Differences between dishwashers and hand washing


Dishwasher detergent

Dishwashers are designed to work using specially formulated dishwasher detergent. Over time, many regions have banned the use of
phosphates in detergent Phosphates in detergent refers to the use of phosphates as an ingredient in a detergent product. The advantage of using phosphates in a consumer laundry detergent or dishwashing detergent is that they make detergents more efficient by chelating c ...
and phosphorus-based compounds. They were previously used because they have properties that aid in effective cleaning. The concern was the increase in
algal bloom An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in freshwater or marine water systems. It is often recognized by the discoloration in the water from the algae's pigments. The term ''algae'' encompas ...
s in waterways caused by increasing phosphate levels (see
eutrophication Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytoplan ...
). Seventeen US states have partial or full bans on the use of phosphates in dish detergent, and two US states (
Maryland Maryland ( ) is a state in the Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware and the Atlantic Ocean ...
and
New York New York most commonly refers to: * New York City, the most populous city in the United States, located in the state of New York * New York (state), a state in the northeastern United States New York may also refer to: Film and television * ...
) ban phosphates in commercial dishwashing. Detergent companies claimed it is not cost effective to make separate batches of detergent for the states with phosphate bans, and so most have voluntarily removed phosphates from all dishwasher detergents. In addition, rinse aids have contained nonylphenol and nonylphenol ethoxylates. These have been banned in the European Union by EU Directive 76/769/EEC. In some regions depending on water hardness a dishwasher might function better with the use of a dishwasher salt.


Glassware

Glassware washed by dishwashing machines can develop a white
haze Haze is traditionally an atmospheric phenomenon in which dust, smoke, and other dry particulates suspended in air obscure visibility and the clarity of the sky. The World Meteorological Organization manual of codes includes a classificatio ...
on the surface over time. This may be caused by any or all of the below processes, of which only the first is reversible: ; Deposition of minerals: Calcium carbonate (
limescale Limescale is a hard, chalky deposit, consisting mainly of calcium carbonate (CaCO3). It often builds up inside kettles, boilers, and pipework, especially that for hot water. It is also often found as a similar deposit on the inner surfaces of o ...
) in hard water can deposit and build up on surfaces when water dries. The deposits can be dissolved by vinegar or another acid. Dishwashers often include
ion exchange Ion exchange is a reversible interchange of one kind of ion present in an insoluble solid with another of like charge present in a solution surrounding the solid with the reaction being used especially for softening or making water demineralised, ...
device to remove calcium and magnesium ions and replace them with sodium. The resultant sodium salts are water soluble and don't tend to build up. ; Silicate filming, etching, and accelerated crack corrosion: This film starts as an iridescence or "oil-film" effect on glassware, and progresses into a "milky" or "cloudy" appearance (which is not a deposit) that cannot be polished off or removed like limescale. It is formed because the detergent is strongly alkaline (basic) and glass dissolves slowly in alkaline aqueous solution. It becomes less soluble in the presence of silicates in the water (added as anti-metal-corrosion agents in the dishwasher detergent). Since the cloudy appearance is due to nonuniform glass dissolution, it is (somewhat paradoxically) ''less'' marked if dissolution is higher, i.e. if a silicate-free detergent is used; also, in certain cases, the etching will primarily be seen in areas that have microscopic surface cracks as a result of the items' manufacturing. Limitation of this undesirable reaction is possible by controlling water hardness, detergent load and temperature. The type of glass is an important factor in determining if this effect is a problem. Some dishwashers can reduce this etching effect by automatically dispensing the correct amount of detergent throughout the wash cycle based on the level of water hardness programmed. ; Dissolution of lead: Lead in
lead crystal Lead glass, commonly called crystal, is a variety of glass in which lead replaces the calcium content of a typical potash glass. Lead glass contains typically 18–40% (by weight) lead(II) oxide (PbO), while modern lead crystal, historically ...
can be converted into a soluble form by the high temperatures and strong alkali detergents of dishwashers, which could endanger the health of subsequent users.


Other materials

Other materials besides glass are also harmed by the strong detergents, strong agitation, and high temperatures of dishwashers, especially on a hot wash cycle when temperatures can reach 75 °C (167 °F). Aluminium, brass, and copper items will discolor, and light aluminum containers will mark other items they knock into. Nonstick pan coatings will deteriorate. Glossy, gold-colored, and hand-painted items will be dulled or fade. Fragile items and sharp edges will be dulled or damaged from colliding with other items or thermal stress. Sterling silver and pewter will oxidize and discolour from the heat and from contact with metals lower on the
galvanic series The galvanic series (or electropotential series) determines the nobility of metals and semi-metals. When two metals are submerged in an electrolyte, while also electrically connected by some external conductor, the less noble (base) will experience ...
such as stainless steel. Pewter has a low melting point and may warp in some dishwashers. Glued items, such as hollow-handle knives or wooden
cutting board A cutting board (or chopping board) is a durable board on which to place material for cutting. The kitchen cutting board is commonly used in preparing food; other types exist for cutting raw materials such as leather or plastic. Kitchen cutting b ...
s, will melt or soften in a dishwasher; high temperatures and moisture damage wood. High temperatures damage many plastics, especially in the bottom rack close to an exposed
heating element A heating element converts electrical energy into heat through the process of Joule heating. Electric current through the element encounters resistance, resulting in heating of the element. Unlike the Peltier effect, this process is independ ...
(many newer dishwashers have a concealed heating element away from the bottom rack entirely). Squeezing plastic items into small spaces may cause the plastic to distort in shape.
Cast iron Cast iron is a class of iron–carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impuriti ...
cookware Cookware and bakeware is food preparation equipment, such as cooking pots, pans, baking sheets etc. used in kitchens. Cookware is used on a stove or range cooktop, while bakeware is used in an oven. Some utensils are considered both cookware ...
is normally seasoned with oil or grease and heat, which causes the oil or grease to be absorbed into the pores of the cookware, thereby giving a smooth relatively non-stick cooking surface which is stripped off by the combination of alkali based detergent and hot water in a dishwasher. Knives and other cooking tools that are made of
carbon steel Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states: * no minimum content is specified or required for chromium, cob ...
, semi-stainless steels like D2, or specialized, highly hardened cutlery steels like ZDP189 corrode in the extended moisture bath of dishwashers, compared to briefer baths of hand washing. Cookware is made of
austenitic Austenite, also known as gamma-phase iron (γ-Fe), is a metallic, non-magnetic allotrope of iron or a solid solution of iron with an alloying element. In plain-carbon steel, austenite exists above the critical eutectoid temperature of 1000 ...
stainless steels, which are more stable. Items contaminated by chemicals such as wax, cigarette ash, poisons, mineral oils, wet paints, oiled tools, furnace filters, etc. can contaminate a dishwasher, since the surfaces inside small water passages cannot be wiped clean as surfaces are in hand-washing, so contaminants remain to affect future loads. Objects contaminated by
solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
s may explode in a dishwasher.


Environmental comparison

Dishwashers use less water, and therefore less fuel to heat the water, than hand washing, except for small quantities washed in wash bowls without running water. Hand-washing techniques vary by individual. According to a peer-reviewed study in 2003, hand washing and drying of an amount of dishes equivalent to a fully loaded automatic dishwasher (no cookware or bakeware) could use between of water and between 0.1 and 8 kWh of energy, while the numbers for energy-efficient automatic dishwashers were and 1 to 2 kWh, respectively. The study concluded that fully loaded dishwashers use less energy, water, and detergent than the average European hand-washer. For the automatic dishwasher results, the dishes were not rinsed before being loaded. The study does not address costs associated with the manufacture and disposal of dishwashers, the cost of possible accelerated wear of dishes from the chemical harshness of dishwasher detergent, the comparison for cleaning cookware, or the value of labour saved; hand washers needed between 65 and 106 minutes. Several points of criticism on this study have been raised. For example,
kilowatt hour A kilowatt-hour ( unit symbol: kW⋅h or kW h; commonly written as kWh) is a unit of energy: one kilowatt of power for one hour. In terms of SI derived units with special names, it equals 3.6 megajoules (MJ). Kilowatt-hours are a common ...
s of electricity were compared against energy used for heating hot water without taking into account possible inefficiencies. Also, inefficient handwashings were compared against optimal usage of a fully loaded dishwasher without manual pre-rinsing that can take up to of water. A 2009 study showed that the microwave and the dishwasher were both more effective ways to clean domestic sponges than handwashing.


Adoption


Commercial use

Large heavy-duty dishwashers are available for use in commercial establishments (e.g. hotels, restaurants) where many dishes must be cleaned. Unlike a residential dishwasher, a commercial dishwasher does not utilize a drying cycle (commercial drying is achieved by heated ware meeting open air once the wash/rinse/sanitation cycles have been completed) and thus are significantly faster than their residential counterparts. Washing is conducted with 65–71 °C / 150–160 °F temperatures and sanitation is achieved by either the use of a booster heater that will provide the machine 82 °C / 180 °F "final rinse" temperature or through the use of a chemical sanitizer. This distinction labels the machines as either "high-temp" or "low-temp". Some commercial dishwashers work similarly to a commercial
car wash A car wash, carwash, or auto wash is a facility used to clean the exterior, and in some cases the interior of motor vehicles. Car washes can be self-service, full-service (with attendants who wash the vehicle), or fully automated (poss ...
, with a pulley system that pulls the rack through a small chamber (known widely as a "rack conveyor" systems). Single-rack washers require an operator to push the rack into the washer, close the doors, start the cycle, and then open the doors to pull out the cleaned rack, possibly through a second opening into an unloading area. In the UK, the
British Standards Institution The British Standards Institution (BSI) is the national standards body of the United Kingdom. BSI produces technical standards on a wide range of products and services and also supplies certification and standards-related services to business ...
set standards for dishwashers. In the US,
NSF International NSF (an initialism for National Sanitation Foundation) is a product testing, inspection, certification organization with headquarters in Ann Arbor, Michigan. NSF also offers consulting and training services worldwide. History NSF Internatio ...
(an independent not-for-profit organization) sets the standards for wash and rinse time along with minimum water temperature for chemical or hot-water sanitizing methods. There are many types of commercial dishwashers including under-counter, single tank, conveyor, flight type, and carousel machines. Commercial dishwashers often have significantly different plumbing and operations than a home unit, in that there are often separate sprayers for washing and rinsing/sanitizing. The wash water is heated with an in-tank electric heat element and mixed with a cleaning solution, and is used repeatedly from one load to the next. The wash tank usually has a large strainer basket to collect food debris, and the strainer may not be emptied until the end of the day's kitchen operations. Water used for rinsing and sanitizing is generally delivered directly through building water supply, and is not reusable. The used rinse water empties into the wash tank reservoir, which dilutes some of the used wash water and causes a small amount to drain out through an overflow tube. The system may first rinse with pure water only and then sanitize with an additive solution that is left on the dishes as they leave the washer to dry. Additional soap is periodically added to the main wash water tank, from either large soap concentrate tanks or dissolved from a large solid soap block, to maintain wash water cleaning effectiveness.


Alternative uses

Dishwashers can be used to cook foods at low temperatures (e.g. dishwasher salmon). The foods are generally sealed in canning jars or oven bags since even a dishwasher cycle without soap can deposit residual soap and rinse aid from previous cycles on unsealed foods. Dishwashers also have been documented to be used to clean potatoes, other root vegetables, garden tools, sneakers or trainers, silk flowers, some sporting goods, plastic hairbrushes, baseball caps, plastic toys, toothbrushes, flip-flops, contact lens cases, a mesh filter from a range hood, refrigerator shelves and bins, toothbrush holders, pet bowls and pet toys. Cleaning vegetables and plastics is controversial since vegetables can be contaminated by soap and rinse aid from previous cycles and the heat of most standard dishwashers can cause BPA or phthalates to leach out of plastic products. The use of a dishwasher to clean greasy tools and parts is not recommended as the grease can clog the dishwasher.


See also

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Home appliance A home appliance, also referred to as a domestic appliance, an electric appliance or a household appliance, is a machine which assists in household functions such as cooking, cleaning and food preservation. Appliances are divided into three ...
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Washing machine A washing machine (laundry machine, clothes washer, washer, or simply wash) is a home appliance used to wash laundry. The term is mostly applied to machines that use water as opposed to dry cleaning (which uses alternative cleaning fluids and ...


References


External links


"How Dishwashers Work"
at
HowStuffWorks HowStuffWorks is an American commercial infotainment website founded by professor and author Marshall Brain, to provide its target audience an insight into the way many things work. The site uses various media to explain complex concepts, termino ...
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