About 68 percent of American homes have a dishwasher, with half of these households using the appliance about one to six times per week. Lower-income and smaller households reportedly use their dishwasher less frequently, according to U.S. Energy Information Administration’s Residential Energy Consumption Survey (RECS).
Backed by research, it turns out that using the dishwasher can save you not just time but dollars on your utility bills as well. Hand-washing can use up more than thrice the amount of water used in the dishwasher, according to Review.com. The University of Bonn also discovered that hand-washing takes up 3.5 kWh of electricity, thrice what’s used in the dishwasher.
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. This device was both slow and unreliable. Another patent granted to L.A. Alexander in 1865 was similar to the first but featured a hand-cranked rack system. Neither was practical or widely accepted.
The most successful of the hand-powered dishwashers was invented in 1887 by Josephine Cochrane and mechanic George Butters in Josephine’s tool shed in Shelbyville, Illinois. Cochrane (a wealthy socialite) wanted to protect her china while it was being washed, so her inspiration was her frustration at the damage to her good china that occurred when her servants handled it during cleaning. 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. This machine is what everyone now knows as the washing machine.
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 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.
Despite this, Liven’s design did not become a commercial success. 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 shape 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 features in dishwashers. One feature was the use of “soil sensors,” 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, then the soil sensor would report the dishes being cleaned. 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 saves energy and water by only being in operation for as long as needed.
Size and capacity
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 inches (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 that allows 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. Glassware, cups, and saucers are placed in the upper rack.
One notable exception was 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 the 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 the back wall of the dishwasher leaving both racks unimpeded. 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 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 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 number 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 detects 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 accidentally starting or stopping the wash cycle. 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.
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.
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 an NSF International testing protocol which confirms the cleaning and sanitation performance of the unit.
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 on a smaller surface area.
They may not dry properly compared to china and glass, which also store more heat. Some dishwashers incorporate a fan to improve drying. Older dishwashers with a visible heating element (at the bottom of the wash cabinet and 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.
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.
Seventeen US states have partial or full bans on the use of phosphates in dish detergent and two US states (Maryland and New York) ban phosphates in commercial dishwashing. Detergent companies claim 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.
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 and other materials
Glassware washed by dishwashing machines can develop a white haze on the surface over time.
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). Aluminum, 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 faded.
Fragile items and sharp edges will be dulled or damaged from colliding with other items and/or thermal stress. Sterling silver and pewter will oxidize and discolor from the heat and from contact with metals lower on the galvanic series 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 boards, 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 (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 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, 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 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. This is because the surfaces inside small water passages cannot be wiped clean as compared to surfaces in hand-washing. As a result, contaminants may still affect future loads. Objects contaminated by solvents may also explode in a dishwasher.