The eggshell can be the cause of many difficulties when cooking with eggs. I bet you have experienced that the eggshell cracks while you are cooking eggs. There is also nothing worse than when a piece of eggshell lands in the dough. But in fact, the eggshell is absolutely necessary to protect the egg.
The eggshell is made of calcium. A hen produces roughly the same amount of calcium per eggshell regardless of the size of the eggshell.
Therefore, the shell is thicker when the hen is young and lays small eggs - and thinner when the hen is older and lays large eggs.
According to the Danish Technological Institute, CO2 leaks out of the egg over time. This causes the pH value in the egg to rise, and this causes the shell membrane and thus the shell to release from the egg white more easily.
A completely freshly laid egg is therefore harder to shell than an older egg.