A toaster is an electric small appliance designed to expose various types of sliced bread to radiant heat, browning the bread so it becomes toast.

The most common household toasters are the pop-up toaster and the toaster oven. A third type, most commonly found in restaurants, has a metal-mesh conveyor belt that moves the bread past constantly-powered heat elements.

In pop-up or automatic toasters, a single vertical piece of bread is dropped into a slot on the top of the toaster. A lever on the side of the toaster is pressed down, lowering the bread into the toaster and activating the heating elements. The length of the toasting cycle (and therefore the degree of toasting) is adjustable via a lever, knob, or series of pushbuttons, and when an internal device determines that the toasting cycle is complete, the toaster turns off and the toast pops up out of the slots.

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 toasting, 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. Toasters may also be used to toast other foods such as teacakes, toaster pastry, potato waffles and crumpets, though resultant accumulation of fat and sugar inside the toaster can contribute to its eventual failure.

Among pop-up toasters, those toasting two slices of bread are more purchased than those which can toast four.^[1] Pop-up toasters can have a range of appearances beyond just a square box, and may have an exterior finish of chrome, copper, brushed metal, or any color plastic.^[1] The marketing and price of toasters may not be an indication of quality for producing good toast.^[1] A typical modern two-slice pop-up toaster can draw from 600 to 1200 watts.^[2]

Beyond the basic toasting function, some pop-up toasters offer additional features such as:

Toaster ovens are essentially small-scale conventional ovens. A frontal door is opened, horizontally-oriented bread slices (or other food items) are placed on a rack which has heat elements above and below it, and the door is closed. The controls are set and actuated to toast the bread to the desired doneness, whereupon the heat elements are switched off. In most cases the door must be opened manually, though there are also toaster ovens with doors that open automatically. Because the bread is horizontal, a toaster oven can be used to cook toast with toppings, like garlic bread, melt sandwiches, or toasted cheese. Toaster ovens are generally slower to make toast than pop-up toasters, taking 4–6 minutes as compared to 2–3 minutes.^[1] In addition to the automatic-toasting settings, toaster ovens typically have settings and temperature controls to allow use of the appliance as a small oven.

Extra features on toaster ovens can include:

Conveyor toasters are designed to make many slices of toast and are generally used in the catering industry, restaurants, cafeterias, institutional cooking facilities, and other commercial food service situations where constant or high-volume toasting is required. Bread is toasted at a rate of 300–1600 slices an hour; the doneness control on such a toaster adjusts the conveyor speed, thus altering the time during which the bread is near the heat elements. Conveyor toasters have been produced for home use; in 1938, for example, the Toast-O-Lator went into limited production.^[3]

Before the development of the electric toaster, sliced bread was toasted by placing it in a metal frame or on a long-handled toasting-fork^[4] and holding it near a fire or over a kitchen grill. Utensils for toasting bread over open flames appeared in the early 19th century, including decorative implements made from wrought iron.^[5]

The first electric bread toaster was invented by Alan MacMasters in Edinburgh, Scotland in 1893.^[6][7]

The primary technical problem at the time was the development of a heating element which would be able to sustain repeated heating to red-hot temperatures without either breaking or becoming too brittle. A similar technical challenge had recently been surmounted with the invention of the first successful incandescent lightbulbs by Joseph Swan and Thomas Edison. However, the light bulb took advantage of the presence of a vacuum, something that couldn't be used with the toaster.

Macmasters' toaster was commercialized by the Crompton, Stephen J. Cook & Company of the UK as a toasting appliance called the Eclipse. 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 problem of the heating element was solved in 1905 by a young engineer named Albert Marsh who designed an alloy of nickel and chromium, which came to be known as Nichrome.^{[8][9][10][11]}

The first US patent application for an electric toaster was filed by George Schneider of the American Electrical Heater Company of Detroit in collaboration with Marsh.^[9][12] 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.^[10]

The first commercially successful electric toaster was introduced by General Electric in 1909 for the GE model D-12.^[9][13][14]

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.^[15] 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.^[16]

The automatic pop-up toaster, which ejects the toast after toasting it, was first patented by Charles Strite in 1921.^[17] In 1925, using a redesigned version of Strite's toaster, the Waters Genter Company introduced the Model 1-A-1 Toastmaster,^[18] 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 the middle of the 20th century, some high-end U.S. toasters featured automatic toast lowering and raising, with no levers to operate — simply dropping the bread into one of these "elevator toasters", such as the Sunbeam Radiant Control toaster models made from the late 1940s through the 1960s, began the toasting cycle. These toasters use the mechanically multiplied thermal expansion of the resistance wire in the center element assembly to lower the bread; the inserted slice of bread trips a lever switch to activate the heating elements, and their thermal expansion is harnessed to lower the bread.

When the toast is done, as determined by a small bimetallic sensor actuated by the heat passing through the toast, the heaters are shut off and the pull-down mechanism returns to its room-temperature position, slowly raising the finished toast. This sensing of the heat passing through the toast means that regardless of the color of the bread—white or wholemeal—or its initial temperature—even frozen—the bread is always toasted to the same degree.

Toasters cause nearly 800 deaths annually due to electrocution and fires.^[19] Poking knives and other objects into a toaster is dangerous; aside from a risk of electrocution, such insertion can damage the toaster in ways that can increase the risk that the toaster will later start a fire.^[20] Even without such tampering, toasters can cause house fires.^[21]

A number of projects have added advanced technology to toasters. In 1990, Simon Hackett and John Romkey created "The Internet Toaster," a toaster which could be controlled from the Internet.^[22] 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.^[23] The toaster dials a pre-coded phone number to get the weather forecast.^[24]

In 2005, Technologic Systems, a vendor of embedded systems hardware, designed a toaster running the NetBSD Unix-like operating system as a sales demonstration system.^[25] In 2012, Basheer Tome, a student at Georgia Tech, designed a toaster using color sensors to toast bread to the exact shade of brown specified by a user.^[26]

A toaster which used Twitter was cited as an early example of an application of the Internet of Things.^[27][28] Toasters have been used as advertising devices for online marketing.^[29]

With permanent modifications, a toaster oven can be used as a reflow oven for the purpose of soldering electronic components to circuit boards.^[30][31]

A hot dog toaster is a variation on the toaster design; it will cook hot dogs without use of microwaves or stoves. The appliance looks similar to a regular toaster, except that there are two slots in the middle for hot dogs, and two slots on the outside for toasting the buns.