Light scattering. Molecular size. Wavelengths. And how physics and chemistry turn transparent egg white to opaque white.
Whenever I am cooking sunny side up eggs (my favorite breakfast) or Eggs Benedict (my favorite brunch), I love watching the transparent egg “white” turn white. That is because the change tells me my eggs are done, and I can dig in very soon (nom nom nom!).
This change happens because the proteins in the egg white denature (i.e. lose their structure), becoming an amorphous semisolid filled with water (read all about the chemistry in the 1-Minute NomNom “Fear and loving in Las Egg-as“).
The chemistry of denaturation is fascinating, but it is not the whole story. There is more, and it has to do with the physics of light and wavelengths.
When light falls on and into any material, its wavelengths are reflected and deflected by the particles on and in the material. This is called light scattering. When the scattered light enters our eyes, we see the objects around us.
For this to happen, the particles must be large enough to scatter the light’s wavelengths. In its raw form, the size of the egg white proteins are pretty small. For example, ovalbumin, the main protein in egg white, has dimensions of 3-7 nanometers (one nanometer is one-billionth of a meter).
This is much smaller than any of the wavelengths of light, which are between 390 and 700 nanometers in the visible light spectrum. Hence, light simply passes through, and the egg white looks transparent.
When the proteins denature, they form a large amorphous semisolid. The size of the protein molecules are now much larger, eventually becoming big enough to scatter and deflect light. As they do so, the transparent egg white turns into opaque white, which is the color we see when most of the wavelengths of light that fall on an object are reflected or deflected.
Egg white turning opaque white is an example of both physics and chemistry phenomena. While we often learn these two areas of science separately, it is often more fun to see how they work in tandem to give us the extraordinary phenomena around us.
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