Modern toasters are typically one of three varieties: pop-up toasters, toaster ovens and conveyor toasters.
In pop-up or automatic toasters, bread slices are inserted vertically into slots (generally only large enough to admit a single slice of bread) on the top of the toaster. A lever on the side of the toaster is depressed, activating the toaster. When an internal device determines that the toasting cycle is complete, the toaster turns off and the toast pops up out of the slots. The heating elements of a pop-up toaster are usually oriented vertically, parallel to the bread slice - although there are some variations.
In earlier days, the completion of the toasting operation was determined by a mechanical clockwork timer; the user could adjust the running time of the timer to determine the degree of "doneness" of the toast, but the first cycle produced less toasted toast than subsequent cycles because the toaster was not yet warmed up. Toasters made since the 1930s frequently use a thermal sensor, such as a bimetallic strip, located close to the toast. This allows the first cycle to run longer than subsequent cycles. The thermal device is also slightly responsive to the actual temperature of the toast itself. Like the timer, it can be adjusted by the user to determine the "doneness" of the toast.
By comparison, toaster ovens are small electric ovens with a door on one side and a tray within. To toast bread with a toaster oven, one lays down slices of bread horizontally on the tray, closes the door, and activates the toaster, usually by means of a lever. When the toast is done, the toaster turns off, but the door must be opened manually. Most toaster ovens are significantly larger than toasters, but are capable of performing most of the functions of electric ovens, albeit on a much smaller scale. They can be used to cook toast with toppings, like garlic bread or cheese, though they tend to produce drier toast and require longer operating times, since their heating elements are located further from the toast (to allow larger items to be cooked). They may also heat less evenly than either toasters or larger electric ovens, and some glass cookware cannot be used in them.
Conveyor toasters are designed to make many slices of toast and are generally used in the catering industry, being suitable for large-scale use. Bread is toasted 350-900 slices an hour, making conveyor toasters ideal for a large restaurant that is constantly busy with growing demand. However, such devices have occasionally been produced for home use as far back as 1938, when the Toast-A-Lator went into limited production.
As with so many home appliances, more elaborate toasters and toaster ovens now utilize computer-controlled mechanisms in place of electromechanical controls. Toasters are usually freestanding, counter-top appliances, although some toaster ovens may be hung beneath cabinets.
Sometimes toast gets stuck in a toaster, particularly pop-up toasters, and must be freed manually. As most toasters are in the kitchen, metal knives and forks are typically an easily available tool but can cause risk of electric shock, unless the appliance is disconnected from the mains.
Some toasters also have a small round griddle on them for making eggs with toast.
Before the development of the electric toaster, sliced bread was toasted by placing it in a metal frame and holding it over a fire or by holding it near to a fire using a long-handled fork. Simple utensils for toasting bread over open flames go back at least 200 years, and earlier people simply speared bread with a stick or knife and held it over a fire.
In 1922, American metallurgist Albert Marsh (1877–1944) of Detroit, Michigan, and his employer, American chemist, electrical engineer, inventor and entrepreneur William Hoskins (1862–1934) of Chicago, Illinois, invented (and in 1906 patented) chromel (later and still today marketed as nichrome), an alloy from which could be made the first high-resistance wire of the sort used in all early electric heating appliances (and many modern ones).
It is unknown who invented the first electric bread toaster. In 1893, Crompton & Company of the UK marketed an electric, iron-wired toasting appliance called the Eclipse, but the device appears to have failed in the marketplace rapidly, as even the Toaster Museum has little information on the device. (Early attempts at producing electrical appliances using iron wiring were unsuccessful, because the wiring was easily melted and a serious fire hazard. Meanwhile electricity was not readily available, and when it was, mostly only at night). The first US patent application for an electric toaster was filed by George Schneider of the American Electric Heater Company of Detriot. AEHC's proximity to Hoskins Manufacturing and the fact that the patent was filed only two months the Marsh patents suggests collaboration and that the device was to use chromel wiring. One of the first applications the Hoskins company had considered for chromel was toasters, but eventually abandoned such efforts to focus on making just the wire itself.
At least two other brands of toasters had been introduced commercially around the time General Electric submitted their first patent application for one, the GE model D-12, in 1909, "the first commercially successful electric toaster".
In 1913 Lloyd Groff Copeman and his wife Hazel Berger Copeman applied for various toaster patents and in that same year the Copeman Electric Stove Company introduced the toaster with automatic bread turner. The company also produced the "toaster that turns toast." Before this, electric toasters cooked bread on one side and then it was flipped by hand to toast the other side. Copeman's toaster turned the bread around without having to touch it. Copeman also invented the first electric stove and the rubber (flexible) ice cube tray.
The next development was the semi-automatic toaster, which turned off the heating element automatically after the bread toasted, using either a clockwork mechanism or a bimetallic strip. However, the toast was still manually lowered and raised from the toaster via a lever mechanism.
The automatic pop-up toaster, which ejects the toast after toasting it, was first patented by Charles Strite in 1921. In 1925, using a redesigned version of Strite's toaster, the Waters Genter Company introduced the Model 1-A-1 Toastmaster, the first automatic pop-up, household toaster that could brown bread on both sides simultaneously, set the heating element on a timer, and eject the toast when finished. By 1950, some high-end U.S. toasters featured automatic toast lowering and raising, with no levers to operate - simply dropping the slices into the machine commenced the toasting procedure. A notable example was the Sunbeam T-20, T-35 and T-50 models (identical except for details such as control positioning) made from the late 1940s through the 1960s, which used a bimetallic beam structure to lower the toast; the inserted slice of bread tripped a lever to switch on the heating elements, and their heat caused the bimetallic pull-down mechanism to lower the bread. When the toast was done, as determined by a small bimetallic sensor actuated by the heat passing through the toast, the heaters were shut off and the pull-down mechanism returned to its room-temperature position, slowly raising the finished toast. As in most such toasters, one sensing unit controls the toasting of two (or four) slices, so the slot with the sensor is marked "ONE SLICE" because operating the toaster without bread in that slot will result in almost immediate shut-off as the heat from the heating element impinges directly on the sensor.
Significant ultramodern chrome designs were the Sunbeam T-9 "Half-Round" or "World's Fair" toaster, designed by George Scharfenberg and introduced in 1939, and the General Electric 139T81, produced in quantity from 1946. Automatic electric toasters were very much a luxury item, with the better models costing up to $25 in 1939 (approximately $360 in 2006 dollars). Most toasters produced from the late 1930s through 1960 are generally considered to be of the highest standard in workmanship and material quality; many were built well enough to last for decades. Due to their aesthetic popularity, some of the classic toaster designs from the 1940s and 1950s are now being reintroduced into the market, though these reproductions for the most part are not constructed to the high standard of the original designs.
More newer additions to toaster technology include wider toasting slots for bagels and thick breads, the ability to toast frozen breads, and a single-side heating mode. Most toasters can also be used to toast other foods such as teacakes, Pop Tarts, and crumpets, though the addition of melted butter and/or sugar to the interior components of automatic electric toasters often contributes to eventual mechanical or electrical failure.
Toasters can be modified to print images and logos on bread slices.
There have been a number of projects adding advanced technology to toasters.
In 1990 Simon Hackett and John Romkey created The Internet Toaster, a toaster which could be controlled from the Internet.
In 2001 Robin Southgate from Brunel University in England created a toaster that could toast a graphic of the weather prediction (limited to sunny or cloudy) onto a piece of bread. The toaster dials a pre-coded phone number to get the weather forecast.
Toaster as terminology apppears in computerspeak. Toasters are commonly used as fictitious computer peripherals for device driver sample code; for example, the Microsoft Windows Driver Development Kit includes a Toaster sample driver. and the original Apple Macintosh computer was sometimes referred to derogatorily as a beige toaster due to its lack of cooling fans.
The Commodore 1541 floppy disk drive was also known among users as the "toaster", due to its internal power source which generated some heat and the term toaster is also used to refer to an email server via which users can retrieve their email using the POP3 or IMAP protocols. Further, Toaster is slang for a recordable optical disc drive; Roxio Toast is one program which works with such devices. The term coaster toaster is also seen, particularly in reference to a drive with a high rate of recording errors.
In Science Fiction, the term Toaster is a common nickname for robots (or similar artificial lifeforms), such as in Star Trek and Battlestar Galactica.
In the area of architecture and design, the New Zealand Railways EF Class (NZR EF class) locomotives are nicknamed toasters, probably because they are currently the only electric locomotives in revenue service, and they have a very boxy shape. In Australia, a multi-level apartment block near the Sydney Opera House is referred to as "The Toaster Building" for its unsympathetic lines in comparison with the more poetic and harbour-referencing Opera House design.