A freshly cracked egg possesses a large ring of thick egg white around the yolk. The longer and above all the warmer the eggs are stored, the more the egg white liquefies. 

With a fresh egg the yolk lies in the centre and with older eggs it moves towards the shell.

The water test: place an egg into a tumbler of water. If it is fresh it lies at the bottom and if it rises to the surface it is older.

After purchase eggs should be placed immediately in the fridge in order to remain fresh for longer. After the sell-by date has expired they should be cooked thoroughly before eating.