A dishwasher is a machine for cleaning dishware and cutlery automatically. Unlike manual dishwashing, which relies largely on physical scrubbing to remove soiling, the mechanical dishwasher cleans by spraying hot water, typically between 45 and 75 °C (110 and 170 °F), at the dishes, with lower temperatures used for delicate items.[1]

A mix of water and dishwasher detergent is pumped to one or more rotating spray arms, which blast the dishes with the cleaning mixture. Once the wash is finished, the water is drained, more hot water enters the tub by means of an electro-mechanical solenoid valve, and the rinse cycle begins. After the rinse cycle finishes and the water is drained, the dishes are dried using one of several drying methods. Typically a rinse-aid, a chemical to reduce surface tension of the water, is used to reduce water spots from hard water or other reasons.[2]

In addition to domestic units, industrial dishwashers are available for use in commercial establishments such as hotels and restaurants, where a large number of dishes must be cleaned.

Washing is conducted with temperatures of 65–71 °C (149–160 °F) and sanitation is achieved by either the use of a booster heater that will provide an 82 °C (180 °F) "final rinse" temperature or through the use of a chemical sanitizer.

A dishwasher has 6 main cycles usually with different options. Rinse and hold is a quick rinse cycle with no drying or detergent for a quick rinse off of dishes. Express is a 60-minute wash usually with drying for washing a small to medium-large load of pre-rinsed dishes. Delicate is for a delicate load of prerinsed dishes. It is an energy efficient cycle. It needs less detergent. It uses mild hot water and a mild dry. Normal is an energy efficient cycle too. It is meant for a regular load of normally stained dishes. It uses mild hot water to save energy and has only 1 or 2 rinses. It has a good drying cycle. Auto or Sensor wash is the recommended wash for most dishes. It uses a turbidity sensor to sense the soil on dishes. it adjusts the water and heat to adapt to the level of soiling on the dishes. This is fairly energy efficient. Heavy is meant for heavily soiled dishes and pots and pans. It also sanitizes the dishes on most dishwashers. It sprays a concentrated hot water jet and a super hot rinse cycle.

Dishwashers also have additional options. Sanitize raises the rinse water to 160 °F (71 °C) and extends the drying time. This is meant for sick people and dishes exposed to raw meat. High temperature wash raises the wash temperature for a better wash. Extra dry makes the dishes dry better.The first mechanical dishwashing device was registered 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.[3]This 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.

However, the most successful of the hand-powered dishwashers was invented in 1887 by Josephine Cochrane together with mechanic George Butters in Josephine's tool shed in Shelbyville, Illinois[4] when Cochrane (a wealthy socialite) wanted to protect her china while it was being washed.[5] Her invention was unveiled at the 1893 World's Fair in Chicago, Illinois 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.[6]Europe's first domestic dishwasher with an electric motor was invented and manufactured by Miele in 1929.[7][8]

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;[9] it included a front door for loading, a wire rack to hold the dirty crockery and a rotating sprayer. Drying elements were even 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 house was becoming increasingly common.[10][11]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 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.[12]In the late 1990s, manufactures began offering various new energy conservation features in dishwashers.[13] One feature was use of "soil sensors", which was a computerized tool in the dishwasher which measured food particles coming from dishes.[13] When the dishwasher had cleaned the dishes to the point of not releasing more food particles, then the soil sensor would report the dishes being cleaned.[13] The sensor operated with another innovation of using variable washing time.[13] 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 saves energy and water by only being in operation for as long as needed.[13]Dishwashers that are installed into standard kitchen cabinets have a standard width and depth of 60 cm (Europe) or 24 inches (US), and most dishwashers must be installed into a hole a minimum of 86 cm (Europe) or 34 inches (US) tall. Portable dishwashers exist in 45 and 60 cm (Europe) or 18 and 24 inch (US) widths, with casters and attached countertops. 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 settings. 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.

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/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 eliminates the inconvenience of the long reach that was necessary with older full-depth models.

Cutlery baskets" are also common. A drawer dishwasher, first introduced by Fisher & Paykel 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, 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 or plastic. Stainless steel tubs resist hard water, and preserve heat to dry dishes more quickly. They also come at a premium price. Older models used baked enamel tubs, while some used a 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.European dishwashers almost universally use two or three spray arms 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 and KitchenAid, 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 arm beneath the upper rack, this allows full use of the bottom rack. Late-model Frigidaire dishwashers shoot a jet of water from the top of the washer down into the upper wash arm, again allowing full use of the bottom rack (but requiring that a small funnel on the top rack be kept clear).Mid-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 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.

Mid-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 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-controlled, sensor-assisted wash cycles that adjust the wash duration to the quantity of dirty dishes (sensed by changes in water temperature) 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 rotary switch often used to control the washing cycle is replaced by a microprocessor, but most sensors and valves 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 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 opening the door during a wash cycle. This prevents accidents with hot water and strong detergents used during the wash cycle.n 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.

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 testing protocol which confirms the cleaning and sanitation performance of the unit.[14]The heat inside the dishwasher dries the contents after the final hot rinse; the final rinse adds a small amount of rinse-aid to the hot water, as this improves drying significantly by reducing the inherent surface tension of the water. Plastic and non-stick items form drops with smaller surface area[15] 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.

North American dishwashers tend to use heat-assisted drying via an exposed element. 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. 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.

Governmental agencies often recommend air-drying dishes by either disabling or stopping the drying cycle to save energy.[16]

Dishwashers are designed to work using specially formulated dishwasher detergent. Over time, many regions have banned the use of phosphates in detergent and phosphorus-based compounds. They were previously used because they have properties that aid in effective cleaning. The concern was the increase in algal blooms in waterways caused by increasing phosphate levels (see eutrophication).[17] Seventeen US states have partial or full bans on the use of phosphates in dish detergent,[18] and two US states (Maryland and New York) 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 (although detergents are typically formulated for local markets), and so most have voluntarily removed phosphates from all dishwasher detergents.[19]

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.