We’ve all been there: trying to peel a hard-boiled egg, but ending up crushing it to bits because the shell stubbornly clings to the white. And it can be even worse, when the egg finds itself covered in small pieces of membrane.
The Internet is full of tips designed to help you avoid this inconvenience, but there are several very different causes that can explain why an egg is difficult to “peel”. Fortunately, science offers strategies to get around the problem.
Factors influencing how easily an egg is peeled
Eggs consist of a hard, porous shell, an outer shell membrane and an inner shell membrane, egg white (or albumen), and a membrane-encased yolk. There is also an air chamber between the two membranes, just under the shell.
In the 1960s and 1970s, much research was conducted on the factors influencing the ease of peeling of eggs after cooking. One of these factors is the pH of the egg white. A 1969 study showed that a pH between 8.7 and 8.9 – therefore quite alkaline – made it easier to peel eggs.
The storage temperature also plays a role. A study published in 1963 found that storage at around 22°C gave better peeling results than storage at 13°C, or refrigerator temperatures of 3 to 5°C.
But we must of course keep in mind that storage at high ambient temperature increases the risk of deterioration (moreover, ANSES recommends always keeping eggs at the same temperature, in order to avoid the phenomenon of water condensation on their surface).
Research has also shown that longer storage time before cooking – meaning less fresh eggs – improves ease of peeling.
Tip #1: Avoid Fresh Eggs
The fact that fresh eggs are more difficult to peel is relatively well known. Based on the factors mentioned above, several explanations make it possible to understand this phenomenon.
First, in a fresh egg, the air chamber is still very small. As the egg ages, it slowly loses moisture through its porous shell, making the air chamber expand as the rest of the contents shrink. A larger air chamber makes it easier to start peeling.
Furthermore, even though egg white is already relatively alkaline to begin with, its pH further increases over time, which also helps make shelling easier.
Tip #2: Water Temperature
Many egg-cooking experts find that starting with boiling water, then bringing it back to a simmer, before carefully dropping the eggs in gives the best results. It is then recommended to use eggs at room temperature to prevent them from cracking due to thermal shock. The idea behind this method is that immediate exposure to high temperature facilitates the separation between the membrane, shell and egg white.
Additionally, a hot start promotes denaturation of egg white proteins (i.e., their structural change under heat), causing them to bind together rather than adhere to the membrane.
After boiling the eggs for the desired time (usually three to five minutes for a runny yolk, six to seven minutes for a creamy yolk, and twelve to fifteen minutes for a hard-boiled egg), they can be immersed in ice water. This helps the white shrink slightly, making peeling easier.
Tip #3 (not required): add ingredients to the water
Other tips suggested to make shelling easier include adding salt to boiling water, but the results need to be nuanced. A study published in 1989 showed that it could indeed improve peeling, but that this effect disappeared after a prolonged period of egg storage.
The addition of acids and bases has also shown some effectiveness in helping to remove the shell. A patent based on this idea therefore proposes using aggressive substances in order to dissolve the shell. But based on this principle, you could simply try adding baking soda or vinegar to the cooking water. In theory, the latter should attack the calcium carbonate in the shell, thus facilitating its removal. As for bicarbonate, being alkaline, it should help detach the membrane from the shell.
Bonus: Some Alternative Cooking Methods
There are several ways to hard-boil eggs aside from classic boiling. Among them: steam cooking under pressure, cooking with hot air (with a air fryera hot air fryer) and even the microwave. In the case of steam cooking, some argue that the water vapor passing through the shell would help loosen the membrane from the egg white, making peeling much easier.
Recent research has focused on air cooking other foods, but it is not yet clear how this cooking method might influence the shell and peelability of eggs.
Finally, once your eggs are peeled, avoid throwing the shells in the trash. They can be used for many purposes: compost, natural repellent against slugs and snails in the garden, small biodegradable pots for seedlings… or even contribute to much more advanced applications, notably in cancer research.
