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The earliest avian eggshells probably lacked pigmentation but, in part to help protect the eggs from predators, many species of bird have evolved a diverse range of coloured shell markings. However, the wide variation in shell colour and pigment pattern arise out of probably no more than three molecules, protoporphyrin, biliverdin and zinc biliverdin chelate. These molecules are constructed from four pyrrole rings (tetrapyrroles) but, while their synthesis pathways are well defined, the site(s) of shell pigment synthesis is less well defined. It is probable that biliverdin is synthesised in the uterus. While there is evidence that protoporphyrin is also synthesised in the uterus the evidence for this is more circumstantial. What is known is that pigment is secreted from the surface epithelial cells of the uterus into the uterine fluid and hence onto the shell. It is notable that the protoporphyrin content the uterine tissue of white-egg laying birds is not dissimilar to that of brown-egg laying birds, the control mechanisms being exerted at the level of protoporphyrin release from the surface epithelial cells into the lumen of the uterus. Similarly white-shelled eggs are not necessarily devoid of pigment. While pigment is normally concentrated on the outer surface of the shell there are many species of bird that incorporate pigment into the outer half or third of the shell. This has stimulated research into potential functional roles for shell pigments, including substituting for calcium carbonate when calcium is limiting and improving shell strength through 'lubricating' the calcite crystals.

Current European Union legislation prohibits the washing of Class A eggs. This is in stark contrast to countries such as the United States of America and, more recently Japan, which have embraced egg-washing technology. The emergence in the UK of egg associated Salmonella enteritidis as a significant cause of food poisoning has, combined with the increase in non-cage egg production systems, increased interest in technologies that might improve the microbial quality of the egg. This paper reviews the history of egg washing in the European Union and more specifically its restricted use in the UK and contrasts this with its uptake in the United States among other countries. Similarly the technological advances in egg washing are reviewed, in the context of the underpinning science.

The potential benefits of washing eggs is offset by a historical perception in the European Union that wetted eggs are prone to spoilage and water loss. This study describes the effects of spray jet washing under various processing conditions to shell surface counts of Salmonella and the presence of bacteria in egg contents. Experiments used eggs that were contaminated with Salmonella Enteritidis PT4 or Salmonella Typhimurium DT104 before cuticle hardening. Washing of contaminated eggs under optimum conditions resulted in a more than 5-log reduction of Salmonella counts from the shell surface. Salmonella was not isolated from the yolk or albumen of any egg washed by the optimal protocol, suggesting that when properly controlled, egg washing did not cause Salmonella to enter the contents. However, contamination did arise if strict control was not maintained over the wash and rinse water temperatures. Both Salmonella Enteritidis and Salmonella Typhimurium were shown to enter the egg contents when water temperatures were lowered, indicating that strict temperature control must be maintained in order to prevent the ingress of Salmonella into egg contents. Other washing machine parameters that were investigated did not significantly affect Salmonella entry into the egg contents but influenced shell surface kill levels to varying degrees.