MadSci Network: Biochemistry

Re: What is the process that changes an egg left in vinegar or salt to a rubber

Date: Wed Feb 17 10:37:09 1999
Posted By: Carl Custer, Staff, Office Public Health & Science, Scientific Research Oversight Staff , USDA FSIS OPHS
Area of science: Biochemistry
ID: 914951025.Bc

Message ID Number: 914951025.Bc
What is the process that changes an egg left in vinegar or salt to a rubber Where can I find out more about this?

I'll answer the second question first because that's what I did first. I wanted to see how frequent this experiment was being carried out and the answer is "a lot".

I used my favorite search engine for science stuff, AltaVista at: I used the following terms: +egg +vinegar +rubber +experiment The"+" requires that term to be in the web page +egg +vinegar would find beau coupe (French for "a lot of") mayonnaise recipes. So, I added +rubber +experiment terms to narrow the search to only 152 pages. I've cited some of them below:
Author: adstaudt
Subject: Rubber Egg
Text: When you soak an egg in vinegar overnight why does it turn to rubber?

Response #: 1 of 1
Author: Joe Schultz
Text: The egg shell is make mostly of calcium carbonate. When soaked in vinegar, which is an acid (acetic acid), the carbonate neutralizes the acid and in the process gets used up. The clear, rubbery 'shell' is the membrane that lines the inside of the egg.


The second question:
What is the process that changes an egg left in vinegar or salt to a rubber

Two things are happening:

  1. the shell dissolves and
  2. the egg white turns to a rubbery substance:
How does 1) happen?
The egg shell is primarily calcium carbonate, the same stuff as chalk. Vinegar is about 6% acetic acid. Acetic acid is a weak acid that is usually made from a special fermentation of wine or apple cider. (acids are sour tasting, for instance the citric acid in lemons, the lactic acid in yoghurt, or the malic acid in apples give those foods their characteristic sour taste- BTW, the German word for acid is "säure") When an acid and calcium carbonate contact, they react and produce:

Carbon dioxide (CO2, a gas which bubbles off), a calcium salt (which may dissolve or precipitate) and water.

So when you immerse an egg in vinegar, the first thing you should see are bubbles of carbon dioxide forming on the egg's surface. For faster results, plop a piece of chalk in a little vinegar.

How does 2) happen? (the egg white turns to a rubbery substance) The answer is more complicated so I'll start with a few facts:

Fast experiment:
Materials: Procedure: See how the controls appear different from the heat or acid treated proteins. Touch the treated and untreated proteins and see how their texture differs. Look up ceviche in an encyclopedia or on the web. Ask an adult to teach you to fry or poach an egg.

Not enough information? You can contact me through the Mad Scientist. Too much? Wait until next year ;^)

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