Harold McGee in On Food and Cooking explains that the white albumen in a fresh eggs has a low relatively low (ie, acidic) pH level. When cooked, these fresh egg whites bond more strongly to the inner shell membrane than it does to itself. As an egg sits in refrigeration for several days, the pH of the white albumen increases and the hard cooked eggs become much easier to peel.
If you get a sudden craving for egg salad and only have fresh eggs in the fridge, McGee suggests adding a half teaspoon of baking soda to the water to raise its pH and also cooking the eggs slightly longer to give the whites time to set firmly. The only downside is that this can make the eggs taste more sulfuric.
vinegar would lower the pH... plus it disolves the shell if there's enough of it, making it thinner and therefore more likely to break while peeling... and it's counter to the recomended "raise the pH" method.
pH of the Water
It's true that over time, acidic liquid can dissolve the shell of an egg, and that alkaline liquid can both make the egg easier to peel, as well as boost that "rotten egg" aroma, but in the short period that an egg spends boiling, pH has little to nothing to do with how the egg cooks. Just use plain tap water; don't bother with vinegar or baking soda
this site has a great breakdown on exactly what happens to an egg while you cook it, and how the white and yolk cook differently.
they also bear out my pet method (starting them in cold water, not hot, and bringing them to a simmer, then putting on a lid and taking them off the heat) gives a more tender less rubbery white... this has to do with heat transfer through the egg, and changes to the white and yolk at different temperatures. the higher the temp of the white, the more rubbery the whites will be.
the heat takes time to transfer from the shell to the center of the yolk to cook it. if you cook it for longer, at lower temps, the whites will be cooler when the yolk reaches a cooked temp. if you cook it faster at a higher temp, by the time the yolk is cooked, the white is at a much higher temperature, and therefore more rubbery.
another site says this about the science - making it more an issue of oxygen and carbon dioxide than of moisture:
http://www.scienceofcooking.com/boiled_eggs.htm
In fresh eggs the albumen sticks to the inner shell membrane more strongly than it sticks to itself because of the more acidic environment of the egg. The white of a freshly laid egg has a pH between 7.6 and 7.9 and an opalescent (cloudy) appearance due to the presence of carbon dioxide. After the protective coat is washed off the egg shell the egg becomes porous and begins to absorb air and loose some carbon dioxide contained in the albumen. This reduces the acidity of the egg which causes (after several days in the refrigerator) the pH to increase to around 9.2. At higher pH the inner membrane does not stick as much to the albumen so the shell peels off easier. In addition, as the egg gets older it will shrink and the air space between the egg shell and the membrane will get larger. Research shows that the reduced acidity helps with peeling.
everything I could find said shocking the eggs after boiling (putting them in icewater until they cool) is important to peelability, but there were several different reasons given as to why.
