The notion that a runny yolk when cracking an egg onto a skillet indicates the egg is old is not entirely accurate. The consistency of the egg yolk is not solely determined by its freshness. Instead, it primarily depends on the temperature at which the egg was stored.
When eggs are refrigerated, the yolk tends to stay more intact, resulting in a thicker and less runny yolk. However, if the eggs are at room temperature or have been stored in a warm environment, the yolk will be more liquid and runny. This is because the proteins in the egg yolk become more fluid as they warm up.
The freshness of an egg can be determined by other factors, such as its smell or appearance. Fresh eggs typically have a neutral odor, while older eggs might have a sulfurous smell. Additionally, as eggs age, the whites become more watery and the yolks can flatten out, but these changes are not directly correlated with the consistency of the yolk when cracked onto a skillet.
To ensure food safety, it's always advisable to check the expiration date on the egg carton and follow proper storage guidelines. When in doubt about an egg's freshness, it's better to err on the side of caution and discard it if there are any concerns.