Toast turns brown as the result of a chemical reaction. Heat from the toaster reacts with the sugars in the bread to produce carbon, which in turn produces the brown and finally black color if the toast is burned.
The reaction responds to the criteria for a chemical change.
- It involves a transfer of energy - heat from the toaster to the bread
- A new substance - carbon - is produced
- The change is irreversible
Brown bread usually toasts faster than white bread because it absorbs more heat than white bread. White bread contains more water and it takes longer to heat.