What makes the bread pop out of a toaster?

When bread is placed in a toaster, an electric current flows through a coiled wire or element inside the toaster that generates heat .This makes the metal coils heat up rapidly, transferring heat to the slices of bread and browning them on both sides. As the heating wire gets too hot , it heats the air in the toaster.

Hot air inside the toaster rises, creating an upward pressure against the lever holding the bread down the upward pressure pushes on the lever, eventually overcoming the spring mechanism and launching the toast into the air when there is enough of pressure.

Some toasters incorporate additional mechanisms known as the toast timer that regulate the duration of heating based on user-selected settings or through built-in sensor to ensure consistent browning and proper timing or the popping action