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Introduction
New Zealand’s estimated 3.2 million laying hens produced around 80.6 million dozen eggs in 2008. This equates to 968 million eggs in total, or 18.6 million eggs a week.
Eggs are mostly produced (created, conveyed, graded and packed) without human handling, except for the removal of undergrades. This means that eggs are therefore less exposed to food safety and hen health hazards associated with more manual systems.
Quality Control
Each hen lays about 300 eggs a year. When the eggs have been collected at the farm, those that are dirty or have cracks or thin shells are discarded. The quality eggs are sent to an egg packing unit where they are graded according to their size:
The grades shown below are based on a minimum size for that standard in New Zealand:
- Jumbo (8): 68g
- Large (7): 62g
- Standard (6): 53g
- Medium (5): 44g
- Pullet (4): 35g
The egg packer also candles the eggs. During candling, the eggs are examined against a bright light. Any eggs with internal or shell blemishes are rejected and used to produce liquid or dried egg.
Egg Shell Colour
Egg shell colour varies from white to caramel brown. Some customers prefer brown eggs
whilst others prefer white, but there is no difference in quality. The difference in shell colour
is controlled by the genetics of the bird. Breeds derived from the Rhode Island Red (such as the Red Shaver and the Hyline Brown) produce brown eggs, and those derived from the Leghorn breed (such as the White Shaver and the Hyline White) produce white eggs. Other colours
can occur but they are unusual; for example, the Araucana from Chile lays blue-green eggs.
Albumen Quality
The white of the egg is made up of two types of albumen that differ in their consistency. One
is jelly-like and is called the thick albumen and the other is more liquid (thin albumen). When eggs are stored, the thick albumen changes enzymatically to a thin albumen, and so customers associate runny whites with older eggs. The albumen becomes thinner as the birds get older, and some hens produce very little thick albumen for genetic reasons.
Yolk Colour
The colour of the yolk depends on what the chicken eats. Feeding maize, for example, can influence the yolk colour.
Double-Yolked Eggs
Double-yolkers are often laid by young birds when they are first coming into lay, and their ovaries are very active. Only a small proportion of hens in a flock will lay double-yolkers, and this is most likely to happen in the eight weeks (or so) from when they first begin laying eggs to when their cycles begin running in a regular rhythm. Some breeds of hen have a higher tendency towards double-yolkers than others. It is estimated that one in a thousand eggs are double-yolkers. In fact, in the UK, in the past, a supermarket chain used to sell cartons of double-yolked eggs!
Double yolkers are more likely to be found in larger size packs, because eggs are graded on weight (as opposed to physical size). They are more commonly found in physically larger eggs (e.g. as found in Jumbo, or Size 8 packs) or in physically smaller eggs which have been packed in with larger-sized eggs (because the double yolk makes the smaller egg more heavy).
An Egg-Within-An-Egg
Have you ever cracked open an egg, only to find a tiny egg inside? While incredibly rare, this can happen! It occurs when a small egg is formed in the oviduct of the hen, which is too small to stimulate the bird into oviposition (laying an egg). So what happens when the next egg is being formed is that the small egg is attached to the interior and is integrated into the growing egg, and the hen then forms a shell around the entire mass.
All About Eggs
In their May and June 2008 editions, Healthy Food Guide published an article called "Back to Basics: All About Eggs". To read information on storage of eggs, testing for freshness and whisking eggs, click on the above link. You can also find information on ways of cooking eggs, including boiling, scrambling, making omelettes, and poaching, along with a number of recipes.
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