Here’s a meal that’s as fun to make as it is easy: eggs in purgatory. It’s pretty much just eggs cooked in a mess of tomato, olive oil, garlic, and basil.
But don’t let the simplicity of the dish fool you. As its epically awesome name suggests, eggs in purgatory is epically delicious. Especially if you add some crispy ciabatta to scoop up those runny yolks and all that tomatoey goodness.
My favorite thing about cooking eggs is watching the transformation as egg whites change from a transparent yellow liquid to an opaque white solid. While it may seem a bit magical, this transformation is the result of a fairly simple biochemical phenomenon known as protein aggregation.
Like we’ve discussed here before, proteins are made up of long chains of amino acids that “fold” into specific three-dimensional structures. The twenty different amino acids have a variety of chemical properties but can be broadly sorted into two groups: hydrophilic and hydrophobic. Hydrophilic amino acids are soluble in water, while hydrophobic amino acids are not.
Generally, a properly folded protein is arranged so that its hydrophobic amino acids are buried and inaccessible to water. The hydrophilic amino acids, on the other hand, remain exposed on the surface of the protein. This allows the protein to be soluble despite having a fairly large proportion of hydrophobic amino acids. If a protein becomes unfolded (aka “denatures”), its hydrophobic residues become exposed to the surrounding water. As a result, the hydrophobic portions of misfolded proteins will stick to one another (aggregate).
An egg white is really just a bunch of proteins in water. When the proteins are properly folded, the egg white appears as a transparent liquid. During cooking, heat causes the proteins in the egg white to unfold and stick to one another. As the proteins become insoluble and aggregate, they solidify and become opaque.
Technically, heat is not the only way to “cook” egg whites. Proteins can also be denatured by the addition of chemicals like salts, acids, and alcohols. Proteins can even be unfolded by the application of electric pulses. This means that you can get the effect (though not the edibility) of a more traditionally cooked egg through some pretty unorthodox methods.