• Question: Why does toast turn black if you burn it

    Asked by desk520muon on 20 Mar 2025.
    • Photo: Sarah Montgomery

      Sarah Montgomery answered on 20 Mar 2025:

      The black part of burnt toast is actually unburnt carbon. If you put it into a hot fire (like on a gas stove), it would eventually burn as well and turn into carbon dioxide gas. It’s common when there is a fire for some unburnt material to be left – if you’ve ever seen a bonfire the next day, you may have noticed a pile of ashes still smouldering the next day and gradually reducing in size as the leftover carbon slowly turns into carbon dioxide. This is also a reason why cars need catalytic converters, to make sure all the fuel is fully burnt rather than being released as unburnt particulates.

Comments

  • Photo: Enrico

    Enrico commented on :

    It’s carbon allotropes. These are black because they are electronically conductive and have high optical absorption. Some scientists have investigated the surface of toast in close detail using electron microscopes and found it contains a wide range of different types of carbon (allotropes). These can include carbon nanotubes and something called bucky balls (fullerene) as well as other polyaromatic hydrocarbons. Most of these aren’t good for you. These are all usually present though only a little bit if the toast is only turned a slight shade of colour, more so as it gets darker. I still like eating toast though! That is also why some people are given dietary restriction to avoid toast and grilled food.