An eggshell is porous. As time passes air works its way in and the air pocket inside grows. The whole freshness test rests on that simple fact.

The water test

Fill a deep glass with water and lower the egg in:

• It lies on the bottom - very fresh.
• It touches the bottom but one end lifts - a week or two old. Perfectly fine to eat.
• It stands upright - old. Use it for boiling, and crack it to check.
• It floats - throw it away.

What you should see when you crack it

The yolk of a fresh egg stands high and the white has two layers: a thick, gathered white around the yolk and a looser ring outside it. As the egg ages the thick white thins and the yolk spreads.

This directly affects recipes where the shape of the egg matters, such as fried eggs and çılbır. In çılbır a fresh egg is almost essential if the poached egg is to hold together.

Older eggs are better for boiling

Unexpected but true: a very fresh egg is hard to peel. The membrane between the shell and the white clings tightly to it, and the white comes away in pieces. In an egg that has sat for a few days the air pocket has grown, so the shell lifts easily.

So if you are making boiled eggs, pick the ones that have been at the back of the fridge.

In the fridge or out of it?

In most countries, Turkey included, eggs are sold unwashed and the natural protective layer on the shell is intact. That is why they can sit at room temperature for a while. The fridge is still safer and extends their life.

One point: eggs straight from the fridge cause problems in cakes and baking, where the mixture splits. Taking them out half an hour beforehand is enough.

The door shelf is the wrong place

The door of a fridge is where the temperature swings most. Keeping eggs on an inner shelf, in their own carton, holds the temperature steady and stops them taking up smells.