EGG PRESERVATION SCIENCE
Eggs can be preserved in many ways, using a simple refrigerator that doesn't do much to the egg, to more chemically dramatic methods, which we are about to describe. Once upon a time, the eggs could be preserved in silicate solution or in lime water. Both solutions would inhibit the growth of bacteria, and make a protective coat around the egg shell. Not too complicated yet...the main point was simply to stop the eggs from drying out by immersing them in special solutions that didn't destroy the egg and also preserved its taste and texture. These techniques became obsolete as we got our refrigerators, but there are still another methods that can be used to not only preserve the eggs but also to change their flavor and color, to a large degree. Interestingly, different techniques have been developed in Western and Eastern continents, so let's discuss some of the most popular ones.
The popular European method is to make pickled eggs. The procedure is as follows. The egg is boiled and then put down in a jar filled with vinegar, some salt, and some aromatic spices. Often, a coloring agent is also added, for example beet juice that will color the egg red. In this condition, the egg can be stored for a couple of weeks, during which the vinegar will break down the egg shell, enter the egg and stay there. What is it good for? The acidic vinegar liquid is preventing bacterial growth, and it also gives a different taste to the egg. So, a simple pickle technique, we might say, as vinegar is used for preservatiion of vegetables as well. Pickled eggs can then be stored for about one year, even without refrigeration, although cold environment is recommended to avoid swelling or cracking of the egg.
A popular Chinese method of storing an egg uses not acid but alkaline liquid instead. Pidan, as the alkali-treated eggs are called, is an ancient way of storing and dramatically changing the egg's taste and colors. The procedure is simple - the egg is immersed in salt and a strong alkaline material, like sodium hydroxide (lye) or the more natural wood ash or lime. Some flavoring agents may also be used, for example green tea. Traditionally, the eggs would be coated in mud that would be allowed to dry out, although this is not necessary, as the egg can just be put down in a solution of the above mentioned agents. In some cases, lead oxide (toxic!) is added to the mixture, which makes the egg yolk softer. Whatever the ingredients are, the result is an egg with brown egg white that becomes jelly-like, and a nice greenish egg yolk. The taste is very eggy, with tones of ammonia and sulfur - created in the process of alkaline solution reacting with the egg proteins. Pidan is a delicacy in China, and you might be served it if you go there!
Other methods of preserving eggs are even more simple. The simplest method by far is just to immerse them in saturated salt solution. The high salt concentration is enough to kill any microbes that could live there. Yet another way to play with egg preservation is to make an alcoholic mixture of fermenting grains and salt and put the eggs in it. After several months, the eggs will become solid and more aromatic, and of course, containing me tones of alcohol!