Heating bread in a toaster and a microwave oven creates very different results. What do microwaves do to bread?
Isabella Van Damme, Arborfield, Berkshire, UK
The results are different because microwaves heat bread from the inside, while a toaster heats from the outside. In a toaster, the bread’s surface quickly reaches temperatures at which the Maillard reaction causes browning and a toasted flavour. Excessive heating can lead to carbonisation or burning.
In contrast, heating a slice of bread in a microwave will dry it out without achieving the surface temperatures required for the browning reactions. Excessive microwave heating can “burn” dry food on the inside without showing any signs on the outside.
Parvez M. Ashraf, Dhaka, Bangladesh
As well as heating only the surface of the bread, using a toaster causes the bread to lose moisture, making it dry and crispy.
In microwave heating, the starch of the bread is re-gelatinised. That is to say, the starch molecules bind to water molecules, which sort of dissolve or plasticise the starch, making the texture of the bread softer overall.
Maria Tsikkinis, London, UK
One of the properties of microwaves is that they are absorbed by water. When bread is irradiated with microwaves, the water in the bread heats up and conducts the heat to the surrounding food.
When the water molecules absorb enough energy, they evaporate, which is why the bread is steaming when you remove it from the microwave and why the slice, soft when you take it out, quickly becomes rock hard once it cools down.
A toaster, on the other hand, uses infrared radiation. These are heat waves and their energy is absorbed by the whole of the bread, rather than just the water.
Theo Megarrity, Brisbane, Australia
“Toasting” toast in the microwave is like trying to start a fire with a pot of boiling water. Microwaves cook through radiation (emitting waves), and toasters cook through proximity to hot elements, which results in the crispy delight that is toast.
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