Before dwelling on the bad egg, which is a rare occurence these days, read some good news about the “slightly older” eggs in your fridge. They are perfect for hard-boiling. They will cook and taste fine . . . and peel much more easily!
If you suspect that an egg is no longer fresh, break it into a saucer and sniff it. A fresh egg, when opened, will smell clean and faintly sweet, if at all, whereas the offensive smell of a bad egg is unmistakable.
You can tell a lot by appearances, too. The white should be translucent, thick and firmly shaped, the yolk smooth and well rounded. Stringy white fibres are often found in the white of a fresh egg. These are quite normal, and their role is to hold the yolk in place in the centre of the egg. As the egg gets older these tend to disappear, allowing the yolk to move about freely inside the shell. If the yolk is flat and the white runs thinly all over the saucer, the egg is definitely past its best.
Any red spots on the yolk have probably been caused by the rupture of a blood vessel during the formation of the egg and will not affect its quality or flavour. Remove the spot with the tip of a spoon if you like.
Whether you’re making a souffle or a batch of bran muffins or anything in between an egg-freshness-check is always prudent.
So give ’em the once-over before you start mixing it up . . .