Do salt or vinegar in the boiling water help peeling eggs?

Question

In another question, a user commented

I've heard some tales that vinegar helps with peeling afterwards

and another one responded

both are totally useless

That struck me as a very good question.

If salt and/or vinegar are added to the boiling water, does that help with the peelability of the boiled eggs? And if there is an effect, how noticeable is it, especially in comparison to other factors such as egg age?

Note that I am not asking about other methods for making eggs easier to peel. Nor is this about the use of vinegar in making poached eggs. I am asking specifically for confirmation or disproval of the salt/vinegar "tale", preferably founded by something more than just "I heard it too".

Answer 1

A chemist here.

I do add baking soda (Sodium bicarbonate). I am satisfied with it as I never got the white stuck to the shell since I do this. However I can't say that the same eggs would have done otherwise without baking soda.

A possibile reason is that the adhesion of the inner coagulated white to the calcium carbonate shell is modulated by pH. In other words rising the pH of the cooking water by a salt with alkaline hydrolysis - such as baking soda - mimicks the conditions of not extra fresh eggs.*

Note that adding table salt (Sodium chloride) cannot work this way as for the pH is let unchanged. I never tried as for I cannot think of an obvious mechansm for why It should work.**

Concerning adding vinegar (a solution of acetic acid in water): the common explaination is that the shell is softened by dissolution. This would also prevent the inner to shell adhesion as well make the shell itself prone to peel off.

I haven't tried this, neither.

*Eggs which are not very fresh undergo changes resulting in a higher pH and are easy to peel.

**The behaviour of proteins is affected by several parameters such as pH, temperature, ionic content. I cannot exclude that adding table salt is indeed effective.

Starting the cooking in already warm tough not necessarily boiling watet is reported effective too. Rationale is that a fast albume coagulation results in the white to inner shrink without setting on the the film near the shell. Worth a try...

Answer 2

Based on what I've read and understand, salt and/or vinegar don't have any effect on how easy an egg is to peel. The most determining factor is age. Here's why.

From Fresh Eggs Daily:

Just under the eggshell is a pair of thin whitish membranes. They help to keep air out of the egg. Once an egg is laid, an air pocket begins to form between the two membranes at the blunt end of the egg. This air sac will continue to grow as the egg ages. Part of the difficulty in peeling fresh hard-boiled eggs stems from the lack of space between the two membranes. Older eggs peel easily because the air between the membranes has begun to separate the egg contents from the shell.

(Picture from different source.)