Toaster elements primarily toast bread through radiation, not by heating the surrounding air. The heating elements inside a toaster are typically made of nichrome wire, which has a high electrical resistance and can generate a significant amount of heat when an electric current passes through it.
When you insert slices of bread into a toaster and activate it, the electric current flows through the nichrome wire elements, causing them to heat up rapidly. These hot elements emit infrared radiation, which is a form of electromagnetic radiation. Infrared radiation is responsible for transferring heat directly to the surface of the bread, causing it to toast.
The process is quite efficient because the infrared radiation is targeted directly at the bread's surface, toasting it evenly and quickly. This is why toasters are much faster at toasting bread compared to conventional ovens, which primarily heat the air to indirectly toast the food.