Test to distinguish between battery and free range eggs without visiting the farm

Scientists have developed a method of determining whether eggs labelled as ‘free range’ or ‘barn’ have, in fact, been laid under battery conditions. The procedure, published in Journal of the science of food and agriculture, means eggs can be tested without the need to visit farms.

The give-away is the dust that the eggs pick up from the surface on which they are laid. Because the eggs are wet when freshly laid, the dust attaches to the shell surfaces. The pattern this creates varies accoring to whether the eggs where laid on cage floors, barn nest boxes or outside. These distinctive patterns can easily be distiguished under ultraviolet light because the dust fluorestes.

The authors found that the prevalence of white double parallel lines with 2.0-2.5 cm spacing was a distinguishing feature for eggs laid on wire floors in cages. They concluded that if five or more eggs in a sample of 90 eggs have double fluorescent lines, there is a greater than 999 in 1000 probability that the batch contains some cage-laid eggs.

The method is effective in distinguishing between free range eggs and those laid on a wire floor cage. It does not damage the eggs and can be applied at any stage in the egg marketing chain.

Washing egg can remove or obscure the double lines, so the authors recommend that in countries where egg washing is common, it is best to perform the test before wasing. Distinguishing features in eggshell fluorescence can be used to identify when eggs have been washed, and they can also be used in preliminary screening tests for sun exposure, which in some countries is a cause of runniness of the egg white.