All the questions you ever had about eggs have finally been cracked.

By Amanda Hoh

How fresh do your eggs need to be to poach them? And how long can you keep eggs before throwing them out?

Eggs are one of the many staples in our diet, but also one of those foods where any change in its structure or age will affect how it cooks and how safe it is to eat.

Gary Kennedy from food standards consultancy firm Correct Food Systems and Rob Peffer, an egg producer from Molong in New South Wales, gave 702 ABC Sydney

Should eggs be stored in the fridge?

It is recommended that eggs are stored in the refrigerator to make them last longer, although a cool pantry can also be suitable.

As an egg ages its enzymes start breaking down the protein structure of the egg white and so keeping them cold means the proteins will last longer.

“The biggest problem for eggs is going up and down in temperature,” Mr Peffer said.

“If you put them in the fridge then pull them out and leave them at 24 degrees and they sweat, that’s worse for the eggs than staying at a stable 18 to 20 degrees.”

Eggs will also last longer if they have been stored in the fridge at the supermarket and then at home.

When should you throw out eggs?

Eggs can last for about six weeks after they are laid, Mr Kennedy says.

After that time the egg “doesn’t perform as well”.

The white might be runny, for example, or will not form firm peaks if you are whipping the egg to make a pavlova or meringue.

What do the numbers stamped on eggs mean?

Some smaller farms like Mr Peffer’s may stamp their eggs with the laying week.

Other producers use extensive coding which could indicate the farm and what shed the eggs came from.

The industry standard is that the stamp identifies the egg grader — the person who sorts the good eggs from the bad ones, Mr Kennedy said.

“If there was any problem anywhere in the system, you could trace the egg all the way back to the farm, to which supermarket it was delivered to.”

Where do you buy the freshest eggs?

“Not the farmer’s market”, according to Mr Kennedy.

“Especially the micro farms which may produce less than 20 dozen eggs, they may be saving up the eggs for one farmer’s market so you’re getting eggs across the entire week.”

Choosing local farms rather than eggs from interstate also means the cartons have gone from farm to shelf faster and are likely to remain fresh for longer.

Less travel time also means reducing the shaking of the eggs which causes the whites to break down.

What egg is best for poaching?

Fresh and smaller-sized eggs are better for poaching.

A larger bird will lay a larger egg which will produce a runnier white.

For hard-boiled, older eggs are best as the shell will peel off more easily.

How fresh is that egg?

To test how fresh an egg is, one age-old technique is to put it in a glass of water, Mr Peffer said.

If the egg sinks, they are fresher than if they float, which indicates there is more air in them and therefore older.

However, Mr Kennedy said the technique wasn’t “perfect” as eggs tended to have air pockets inside them making them float.

He said the “crack technique” was a better measure.

“If you get a really fresh egg and you crack it on a bench top, the white will stay as one.

“But when the egg gets really old, the white will start breaking down and get separated into two distinct fractions — a thicker part and the outside will break down and be really runny and watery, not gel-like.

“The older the egg is, the more likely the outside white is runny.”

This post originally appeared on ABC News.