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.
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.
Among pop-up toasters, those toasting two slices of bread are more purchased than those which can toast four. 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. The marketing and price of toasters may not be an indication of quality for producing good toast. A typical modern two-slice pop-up toaster can draw from 600 to 1200 watts.
Toaster ovens are essentially small-scale conventional ovens and can be used to cook foods other than just toasting. 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. 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.
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.
The primary technical problem in toaster development at the turn of the 20th century was the development of a heating element which would be able to sustain repeated heating to red-hot temperatures without 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 for the 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 a toaster with an automatic bread turner. Before this, electric toasters cooked bread on one side, meaning the bread needed to be flipped by hand in order to cook both sides. Copeman's toaster turned the bread around without having to touch it.
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 type of bread (white or whole grain) or its initial temperature (even frozen), the bread is always toasted to the same consistency.
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. 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.
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.