Egg quality | CSIRO
18 March 2010 | Updated 14 October 2011
"Under no circumstances should eggs for in-shell storage be washed as this removes the surface bloom and makes the eggs more susceptible to attack by microbes"
This fact sheet explains what to look for when assessing the quality of eggs, how to best store them to maintain freshness, and simple steps to avoid the risk of food poisoning from egg dishes.
Egg quality: what to look for
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If you look closely at an egg shell held against a bright light in a dark room you will be able to see an air gap, usually at the blunt end of the egg.
In a fresh egg this air cell is quite small but as the egg ages, water is lost from the 17 000 pores in the egg and the air cell gets larger.
Also you can see a large moving shadow in the egg which is the yolk floating about in the white.
In fresh eggs the yolk is small and in the centre of the egg. If you hard boil an old egg, you can quite clearly see the air cell indentation in the top of the egg.
A quick test for freshness is to check if the raw egg in the shell sinks in a basin of water.
When you cut along this hard boiled egg lengthways you will see that the yolk has moved off centre.
A quick test for freshness is to check if the raw egg in the shell sinks in a basin of water.
Fresh eggs stay at the bottom of the bowl while stale eggs stand on end or float because of the large air cell.
Other factors such as a weak shell and fine cracks may also cause the egg to float.
Good quality, fresh eggs display certain characteristics when broken out.
The yolk is small and rounded and stands high in a thick, gel-like egg white which tends to stay compact rather than spread out over a wide area.
As eggs age, the yolk becomes larger and flatter, until it eventually breaks.
The thick egg white becomes thin and runny. By this time the egg will also have developed a stale odour and flavour.
For long term storage - control the temperature
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The easiest way to maintain eggs at high quality is to store them in cartons in the refrigerator as soon as possible after they are laid.
Clean eggs, free of visible defects of the shell and contents, will then remain at high quality for up to three months and will still be as 'fresh' as eggs stored for seven days at room temperature.
They can be stored for longer periods but the quality will begin to deteriorate noticeably.
The cartons reduce water loss and help prevent flavours from other foods from being absorbed into the eggs.
Only clean, uncracked eggs should be stored.
Dirty eggs should be used immediately or frozen as pulp (see method on the next page).
Under no circumstances should eggs for in-shell storage be washed as this removes the surface bloom and makes the eggs more susceptible to attack by microbes.
Keep dirty or cracked eggs separate to avoid contamination of the clean eggs.
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Oiling of eggs
Where it is difficult to refrigerate eggs a coating of oil may be applied to help preserve them.
Although on its own this is not as effective as refrigeration, it does slow down the loss of quality of the egg and if the eggs are then stored in a cool place you should obtain about three weeks of high quality life in most parts of Australia (in the tropical regions you may only get about two weeks).
Research has shown that if oiling is to have maximum benefit it should be carried out on the day the egg is laid.
One of the following oils may be used but other commercial mineral oils may be suitable:
- paraffin oil
- Ampol technical white oil No. 3
- Caltex White Oil Pharma 15.
This should be applied with a manual pressure spray (similar to that used to mist plants) so that the egg is completely covered with a fine film of oil.
Research has shown that if oiling is to have maximum benefit it should be carried out on the day the egg is laid.
The eggs can then be put in clean cartons and stored until required.
Once again only clean, sound eggs should be used.
Before boiling oiled eggs it is important to prick the shells to allow the air to escape otherwise the eggs will crack open.
Freezing of raw egg
Excess eggs, whose shells are free of cracks, can be frozen as whole egg pulp, egg yolks or egg whites.
Raw egg whites freeze well but yolks undergo gelation and when thawed are thick and gluggy.
Such yolks do not beat well and cakes and other products made from them are disappointing.
The problem can be overcome by lightly beating the egg yolks and whole eggs then adding a small amount of sugar or salt to the eggs before freezing.
Add one teaspoon of salt or one tablespoon of sugar to every six egg yolks or eggs.
Freeze in small amounts of one or two eggs (about 55 g to 100 g).
These should keep in the freezer for up to 10 months.
