May 2011
I never thought that teaching ‘Egg Quality and Bird Handling’ to first year Veterinary Science university students would be so much of a learning experience for me as well.
When cracking eggs onto the glass plate, I posed three questions: would you rather a white or brown shelled egg; would you prefer yellow or orange yolk; and is there any difference?
I usually got standard answers of “brown”, “orange” and “yes, the others are bad”.
My short answer to them - not true, they are all the same when you eat them and here is why.
First, the shell. There are many different colours of egg shells around the world, yet in different countries we have created preferences for a particular type.
In fact, the New York Times reported about egg colour preferences during the First World War! In Australia and the United Kingdom, we have preferences for brown shelled eggs.
In the United States of America, they prefer white shells. It really doesn’t matter which colour it is as it has absolutely no bearing on the quality, taste or nutritional value of the egg.
All eggs are white by default being the colour of the calcium carbonate of which they are made. As the egg travels through the reproductive system, the lining of the oviduct adds pigments to the eggs, which vary in colour depending on the breed of chicken.
This is a trait controlled by the female bird, meaning that the breed of the rooster has no effect on egg colour. Some examples of egg colours and the breeds which produce them are: dark brown speckled egg (Speckledy or Maran), a pure white (White Star or White Leghorn), a pinkish-brown (Rhode Island Red), a creamy white (Ancona or Vorwerk), a mid-brown (ISA Brown, Black Rock or Barnevelder), and a bluish-green (Araucana or Cream Legbar).
Secondly, the yolk. Same as for shell colour, the colour of the yolk does little to give us an indication of quality, taste or nutritional value. Yolk colour is directly related to the amount of yellow/orange pigments (called Xanthophylls) in the diet.
These pigments are found in common feedstuffs such as corn and marigolds. Adding more of these types of feed in the diet of the layer will increase the orange colour of the yolk.
So if we can’t use either of these to assess quality, then what are we really looking for in an egg? It is not easy to outwardly assess the taste or quality of an egg. Obviously we don’t want those with thin shells that will break easily in transit- which will occur as the bird increases in age and has less calcium in her bones to utilise for the shell.
The main indicator of quality is the ability of the albumin (the egg white) to hold together when cracked. The older the egg, the more the proteins that hold the egg white together will have lost their ability to do just this.
The result is that when we crack the egg, the white tends be thin and run. In order to maintain the best quality of the eggs, keep them in the fridge.
This will slow the protein degrading process down and can keep them fresh for more than six weeks.
Remember, we can’t always judge a chook by its cover!
Kiri Broad