Radiation. Absorption. Reflection. And getting the perfect toast.
Every source of heat also radiates light. The wavelengths of light used to cook food are mostly in the microwave and infra-red range, that fall outside the visible spectrum. Toasters, for example, toast bread with infra-red radiation.
Atoms in food absorb some of these light waves and convert the light energy into faster motion or more energetic vibrations. On a macroscopic scale, this is heat.
How much energy the food absorbs depends on two things: how much light it absorbs versus how much it scatters or reflects. This ratio is called reflectivity.
Toast takes much longer to go from white to brown than it does to go from brown to burnt. That’s because when the bread’s surfaces have darkened, its reflectivity falls. The darker it gets, the more energy it absorbs. In fact, a dark side can absorb more than 10 times as much radiant energy from the heating elements as a white surface.
We can see just what this difference means by looking at the timings in the photo above. According to the Modernist Cuisine, it might take 3 minutes for a piece of bread to go from white to brown, but only 30 seconds to go from brown to burnt! So if your bread does not seem toasted yet when it first pops out, pop it back into the toaster, but not for too long!
Tell me how you get your toast just right! Share your photos, experiences and tips with me!
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photos: in order – istockphoto/milosluz; depositphotos/ekostsov; edesignua; Sandralise