June 8, 2008
The Mystery of the Egg Shells
Just about every recipe for making clear broth recommends skimming the fat off the broth, beating one egg white lightly with a bit of water for each quart of broth and adding this to the cool broth together with the crushed egg shells. Then you bring the broth to a boil and wait for the scum to gather all the particles that make the broth turbid. Once the scum has formed, they recommend letting the broth cool before filtering it through cheesecloth. I filter the broth while hot with no ill effect.
I have been following this procedure for years and it works flawlessly unless you add the beaten egg whites to hot broth in which case you get milky egg soup. Lately I have been wondering the purpose of the egg shells, as far as I can tell they don't really help in clarifying the broth. Overcome by curiosity I took to Google, the master of all answers. I drew a blank! No one seems to know why the egg shells are used in clarifying the broth. One person suggested it was a bad idea because they could be the source of salmonella and the resultant food poisoning. I guess this guy or gal never heard of washing the eggs.
Since man has been cooking soup for millennia, my guess is that the answer is lost in the mist of time. Maybe it was a way of fortifying the soup with the calcium of the egg shells.
And so the Mystery of the Egg Shells remains unsolved.
What are egg shells made of?
The main ingredient in eggshells is calcium carbonate (the same brittle white stuff that chalk, limestone, cave stalactites, sea shells, coral, and pearls are made of). The shell itself is about 95% CaCO3 (which is also the main ingredient in sea shells). The remaining 5% includes calcium phosphate and magnesium carbonate and soluble and insoluble proteins.General Chemistry Online!
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