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I know that an egg shell is made up of approximately 92% Calcium Carbonate. The remaining percentage of the mass is a protein matrix. I know that vinegar (5% acetic acid) dissolves the Calcium Carbonate. Does any other food (such as lemon juice or some other acid) dissolve the shell of an egg. If so, how long does the process take?

I want to dissolve the shell of the egg before I soft-cook it.

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Before you soft-cook it? What is that going to get you that cracking the egg wouldn't? –  Jefromi Jun 12 '12 at 4:46
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Science is why. Also cracking the egg risks breaking the inner membrane and leaking the albumen. Dissolving the shell would not dissolve the membrane. –  cytinus Jun 12 '12 at 4:52
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Any acid will do it eventually. I know it takes a few days with vinegar. But you'll need to leave it in the fridge if you intend to eat it, so it'll probably take longer. Also, you're pretty well guaranteed to pick up some flavour from your acid. –  Chris Cudmore Jun 12 '12 at 12:51
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3 Answers

The reason vinegar ruins the naked egg is that the vinegar moves into the egg by osmosis. That's a function of time and of concentration. The longer the egg soaks, the more acid it absorbs. I haven't tried this variation of the experiment yet, but I've made a naked egg for non-cooking purposes. I've been thinking how to do this, and here's what I've got:

1) Use a more concentrated vinegar to weaken the shell faster, so it doesn't soak as long. Be prepared to remove most of the shell by hand when it's weak enough. The egg's membranes should hold up fine if you're careful.

2) Once the shell is sufficiently compromised to allow expansion, try soaking it in distilled (or highly purified) water. The egg will expand, and that should counter some of the osmotic pressure, keeping the vinegar out. It will also make removing shell pieces by hand easier.

Expect it to take a few days. Also, I don't know if you're using supermarket eggs or something sturdier, but the shells on most supermarket eggs are thinner to begin with. I wouldn't try this on a free-range egg from your henhouse.

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My memory of how acids work from high school chemistry is that pretty much any acid will dissolve the shell, eventually, given enough acid. Depending on the concentration, the type, and the volume of the acid, the amount of acid you require will vary though. There will also be variability between eggs; some will have a much thicker shell than others.

If you want to eat the end product, that will of course rule out any acids that aren't food safe.

I disagree with @RossHolloway's answer that the egg will automatically go off because its shell has gone. This site indicates that the shell itself is porous and though they say the shell can block bacteria they also say the inner membranes "provide efficient defense against bacterial invasion".

The next question is whether the acid will also affect the inner membrane (you may want it intact). My link states that the membrane is made of keratin, which is a protein. I suspect it will not dissolve quickly in some weaker types of acid, so it probably is possible to completely dissolve the shell but not the membrane. Maybe someone else can expand on this?

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Raw eggs (without the shell) already keep for a few days in the fridge, and this is true even if you've broken the membrane when you cracked it, so I don't really see why there'd be a safety issue from the amount of time it takes. –  Jefromi Sep 4 '12 at 17:08
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Someone once had me on in a pub that you could pickle eggs by simply placing a raw egg in a jar of vinegar and the energy released by the shell dissolving would hard boil the egg.

When I got back home I put a raw egg in a vinegar filled jar. Immediately air bubbles appeared around the shell as some chemical reaction kicked off.

The shell was completely dissolved in about 3 days. The egg was raw and no doubt gone off since it had been denyed its naturally given vacuum pack, i.e. the shell.

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