The biggest key to decide whether to peel an egg is the egg white.
The fresher an egg is, the harder it is to peel it. Foreign food magazines have suggested that it is perfect to boil eggs in the refrigerator for 7 to 10 days. With the passage of time, many characters of fresh eggs have changed gradually, among which two have the greatest influence on peeling eggs-the first is the pH value of egg white, and the second is the content volume of eggs.
The egg white of fresh eggs just laid contains carbon dioxide produced by previous metabolism, so the egg white is slightly turbid, and the pH value is about 7.6 to 7.9, which is a relatively acidic condition. After coming into the world, eggs can exchange air with the outside world through porous eggshells-inhaling oxygen and releasing carbon dioxide-in fact, eggs are breathing. The loss of carbon dioxide increases the alkalinity of egg white and raises the pH value. Generally, after three days, the pH value of egg white rises to about 9.2. 2 1 day, rising to 9.4. The maximum is 9.7.
As early as in 1959, a researcher named swanson wrote an article entitled "Observation on Fresh Boiled Eggs and Disposal of Boiled Eggs", which accurately pointed out that as long as the pH value of egg white is lower than 8.7, eggshells are difficult to peel off, while it is easy to peel off when it is higher than this value. He also mentioned that as long as fresh eggs are stored at 15 degrees Celsius for 48 hours, the pH value can rise above 8.7. If you are particularly anxious, you can steam your eggs with ammonia water in a closed container for ten minutes, which will soon reach this pH value.
Following swanson, Mien and others in 196 1 year, Reincke and others also studied this problem in 1964, and the "pH value of easy-peeling egg white" is also roughly between 8.7 and 8.9. They also observed under the microscope that the egg membrane that is easy to peel is relatively dense, while the egg membrane that is difficult to peel is relatively loose.
In addition, eggs will gradually lose some water through porous eggshells during storage. So fresh eggs of the same size are always heavier. When placed in water, the freshest eggs will sink, while old eggs will sometimes float. The loss of water directly leads to the reduction of the contents of eggs, which provides an expanding space for the air chamber between eggs and eggshells, and forms a tiny gap between the inner and outer membranes, which naturally helps us peel eggs.