Adding salt or acid to water doesn't actually make eggs easier to peel. What does help: using older eggs (7-10 days old) and shocking them in ice water after cooking.
Boiled egg peeling is a problem with a well-understood solution that most people ignore in favor of popular but ineffective tips. The common advice about adding salt or vinegar to boiling water persists because it contains a grain of plausibility: acid can coagulate egg white that leaks through a cracked shell, preventing the white from spreading through the water. That is a different problem from peeling difficulty. What actually determines how easily an egg peels is the age of the egg and the cooling method used after cooking. These two variables explain nearly all the variance in peeling outcomes.
## The Physical Cause of Difficult Peeling
The inner shell membrane adheres to the egg white. In a fresh egg (1 to 3 days old), the white has a low pH of about 7.6 and the proteins are tightly structured. At this pH, the white protein adheres strongly to the inner membrane. When you try to separate the shell and membrane from a freshly boiled egg, the membrane tears into the white, and the white tears with it, leaving a cratered surface.
As an egg ages, CO2 escapes through the shell pores and the pH of the white rises to 9.0 or higher. At this more alkaline pH, the protein structure of the white changes: the proteins are less sticky, the gel is slightly softer, and crucially, the adhesion between the white and the inner membrane decreases. When you peel a 7 to 10 day old boiled egg, the membrane releases cleanly from the white, producing a smooth surface.
## The Role of the Ice Bath
The second critical variable is the ice bath immediately after cooking. Rapid cooling causes the egg white to contract away from the shell membrane. This physical contraction creates a slight separation between the white and the membrane, making it easier to slip a finger or spoon under the membrane to start the peel. Eggs left to cool slowly in hot water or at room temperature do not contract as decisively and tend to re-adhere to the membrane as they cool.
The ice bath also stops cooking immediately, preventing the formation of the green iron sulfide ring around the yolk. Beyond freshness and rapid cooling, the cooking method has some effect: eggs steamed rather than boiled peel somewhat more reliably because steam penetrates the shell differently, but the effect is secondary to egg age and cooling speed.
## Why Salt and Vinegar Don't Help (And What They Do)
Salt in boiling water does raise the boiling point of water by a trivially small amount and has no meaningful effect on egg protein structure or membrane adhesion. The myth persists because salt is used during boiling for many other foods and carries a general reputation for improving outcomes. Vinegar (acid) in boiling water does slightly affect the outermost layer of egg white if the shell cracks during boiling, coagulating the leaking white and keeping the egg intact. This is a different goal than easy peeling.
Some cooks report success with pricking the blunt end of the egg with a pin before boiling. This allows steam to escape from the air cell during initial heating, reducing the likelihood of the shell cracking. A cracked shell during boiling can cause the white to bond unevenly to the membrane, making peeling harder.
For consistent results: use eggs that have been refrigerated for at least 7 days, boil or steam them as usual, and transfer immediately to ice water for at least five minutes before peeling. Start peeling at the blunt end where the air cell is located, as that end typically peels most cleanly.