The smell of rotting eggs is one that’s immediately recognizable, that acrid, sulfuric smell that doesn’t seem to have a counterpart with any other food. But why, exactly, do rotting eggs have such a unique and horrible smell?
Eggs are very high in two proteins, globulin and keratin. When globulin begins to decay, a toxic chemical is released that’s called hydrogen sulfide, which has that very potent sulfur smell. Keratin also has very high levels of an amino acid called cysteine, which is full of sulfur atoms. When the keratin begins to break down, out comes the cysteine. Both of these proteins release that sulfurous smell, resulting in an odor that immediately tells you that this egg has gone bad.
By the way, even though most European supermarkets don’t refrigerate eggs, if you want your eggs to last longer always make sure they’re refrigerated. And don’t take them out of the carton and put them in the egg compartment in the refrigerator door; leave them in the carton and store the eggs in a part of the fridge that stays consistently cold.