Candling: The quality of the egg in the shell is evaluated by candling. The egg is held against a source of strong light. Candling will reveal:
A crack in the shell.
The size of the air cell.
The firmness of albumin.
The position and mobility of yolk
The possible presence of foreign substances like blood spots, moulds and developing embryo.
As the eggs deteriorate, the chalaza weakens and the yolk tends to settle toward the shell rather than remain suspended in the firm white. Under such circumstances, the yolk is more fully visible when the egg is candled. Dark yolks cast a more distinct shadow than light-colored yolks.
Although candling is the best available method for rating unbroken eggs it may not be totally reliable.
Floating in water: If the egg sinks it is considered as good. Poor quality eggs float due to increase in size of the air cell and due to loss of moisture.
Haughs Unit: Measurement of the height of the thick white in relation to the weight of the egg gives haughs unit. Good quality egg has 72 haugh units and as the quality deteriorates it comes down to 30-60. Micrometer is used to measure the height of thick white.
White Index: The height of the thickest portion of the white is divided by the diameter of the egg gives white index.
Yolk Index: Measurement of the height of the yolk in relation to the width of the yolk gives the yolk index.
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