The cuticle is the outermost layer, deposited on the palisade layer of the eggshell during the last 1.5-2 hr of eggshell formation in utero. It is a non-calcified, thin, water-insoluble layer composed mainly of glycoproteins with some carbohydrate and fat constituents. The cuticle functions as a protective layer which regulates gaseous exchange across the shell, acts as a first line of defence against microbial penetration across the eggshell and is associated with termination of calcite crystal growth during shell formation. The extent of cuticle deposition is influenced by hen age and strain. The physiological and microbiological characteristics of the hen eggshell cuticle are reviewed in relation to its protective functions.

Over the past 40 years there have been many changes in egg production and processing, as well as, the egg itself. Many of these changes have contributed to the microbial challenges of the egg that we face today. Salmonella enterica serovar Enteritidis (SE) and more recently Salmonella enterica serovar Heidelberg (SH) are the two organisms of most concern associated with eggs. Most U. S. egg producers utilize some type of control programme to ensure egg safety. Many use the United Egg Producers' “5-Start” Food Safety Programme. Commercial egg washing significantly reduced concentrations of aerobic bacteria, yeasts and moulds, Enterobacteriaceae, and E. coli on shell egg surfaces. However, refrigeration of eggs is often identified as one the most critical issues in minimizing the risks associated with Salmonella contamination in eggs. The condensation question always arises any time egg refrigeration is discussed. Moisture often condenses on the shell surface when cold eggs are moved from the cool storage into hot and/or humid conditions. Research has shown that the ability of any microbes present on the shell to penetrate the shell was not increased with egg sweating. Also, heat sensitivity of SE can be induced by exposure to low temperatures. Although low numbers of SE and SH can contaminate eggs via the transovarian or shell penetration route, these small numbers cannot be ignored. Storage at temperatures as low 4°C combined with natural defences does not completely prevent growth. Furthermore, rapid growth occurs at 25°C, so minimal temperature abuse could result in high levels of contamination within eggs. The need for proper management during production, properly controlled storage, cooking and serving is critical.

The microbiological implications of using a small-scale bucket-style washer are reported forchicken eggs. On average, the bucket washerreduced the total bacterial numbers on the surface of eggs under manufacturer-recommended conditions from 5.36 log CFU egg-1 to 2.82 log CFU egg-1. No evidence of enhanced bacterial contamination of the egg contents was found when microbiological examination was undertaken a few hours afterwashing. When washing visibly soiled free-range eggs, there was a tendency forthe wash-waterto become dirty afteronly a few batches of eggs had been washed. Washing in dirty water could increase the numbers of bacteria on the surfaces of those shells which were visibly clean before washing. These additional shell-surface bacteria however, were not detected in the egg contents (n=1032), when analyses were undertaken 1–2 hours after washing. In contrast, when washed eggs were stored for2 weeks at 15°C, we found that bacterial numbers in the egg contents were elevated when compared with unwashed controls. To determine if cool washing temperatures could cause water to taken up by egg contents, eggs were warmed to 37°C, 30°C, 25°C or 20°C and were submerged in aqueous protein stain at 15°C forup to 7 minutes. We did not observe take up of the stain solution unless its temperature was 15°C cooler than the egg contents and the eggs were immersed forat least 3 minutes.

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.