Depending on the bird species, about 33-86% of the egg content consists of albumen. In eggs from domestic fowl, albumen contains about 10.5% protein and 88.5% of water and may be regarded as the main water source for the developing embryo. Besides carbohydrates, lipids, and inorganic ions, over 90% of the solids in the albumen are proteins. Several factors are known to influence the amount and composition of the albumen: egg weight, age and genetics of the parent flock, amount and quality of the feed provided, environmental factors (e.g. temperature, light), position in laying sequence, and also storage conditions of eggs prior to incubation. The albumen content of an egg plays an important role during embryonic development. Not only for formation of sub-embryonic fluid, but albumen proteins are known to flow into the amniotic cavity, the yolk sac and finally the digestive tract of the embryo and are used as the main source of proteins for tissue synthesis. Partial removal of albumen had negative consequences on chick weight at hatch, reduced the amount of amniotic and allantoic fluid and may reduce the water content of the chick and the residual yolk. Replacing the removed albumen with saline, however, reduced the residual yolk weight without differences in water content, suggesting increased uptake and utilisation of yolk, possibly as a compensation for the removed albumen proteins. In addition to reduced chick weight at hatch, some authors report an asymmetric growth restriction where nutrients are diverted away from non-vital organs in favour of brain and heart, with a relative ‘sparing’ of these latter two organs. Partial albumen removal led to a reduced whole-body protein synthesis, similar to eggs containing naturally less albumen. Importantly, several studies reported some long-term effects of albumen removal on growth, indicating that prenatal environment will have life-long consequences.

The hen's egg, in the form of table eggs and egg products, forms a staple part of the world's total protein consumption. In the last century, there has been considerable research effort focusing on ways of improving egg production and enhancing the quality of eggs. More recently, and with the development and application of new molecular technologies, our understanding and knowledge of how an egg is formed, what it actually consists of, in terms of its major versus minor components, and what the functional roles of each of these components might be, have been greatly enhanced. For example, new previously unknown molecules with specific activity or functional properties have been discovered in the egg albumen and yolk, some of which have potential uses in pharmaceutical and other food related applications. This review paper, which is the collaborative effort of members of Working Group 4 - Quality of Eggs and Egg Products - of the European Federation of WPSA, describes the scientific research behind a number of these major advances and provides some insight to the focus of current research in this area.

Egg storage is a common and important practice in the poultry industry. Knowledge of the effects of storage on the egg, the embryo and incubation yield is important for planning incubation by hatcheries. Recommendations for storage environmental conditions depend mainly on the breeder age and storage time. Storage from seven days or more alters the characteristics of albumen, reduces incubation yield, increases incubation period and can damage embryonic development. When working with long storage periods, the adoption of management practices such as storing the egg with the thin tip down, egg turning during storage and pre-storage incubation should be considered to reduce the negative effects on the incubation yield.

Excluding disease, the single most important factor affecting the albumen quality of the freshly laid egg is the age of the bird that laid it. With advancing flock age, Haugh unit scores decrease and the variability of the scores increases. An induced pause in egg production is beneficial in largely restoring albumen quality in aging hens. Both strain differences and strain/age interaction effects in Haugh unit scores of fresh eggs have often been observed, but these are normally small and have little practical significance. Albumen quality of the egg is not greatly influenced by bird nutrition. Environment and housing, even heat stress, appear to have almost no direct effect on the albumen quality of the egg at oviposition.

When ambient temperatures are high, delays in egg collection and/or cooling increase the rate of Haugh unit score decline. The maintenance of albumen quality during egg storage is dependent on the eggs being cooled quickly following lay and subsequently being held at low temperatures, preferably down to, but not below, 0°C. Oiling of eggs within 24 h of lay is very effective in retarding deterioration of the albumen but does not replace the need for cool storage. Information on genetic effects on the albumen quality of stored eggs is equivocal, although there is general agreement that any effects are small and of little commercial significance. Of greater importance is the finding that within strains there can be great variation in Haugh unit scores and that strains laying white-shelled eggs are much less variable than those producing brown-shelled eggs.

The literature concerning the influence of ahemeral light cycles on the quality of eggs is reviewed. Results pooled from published reports were used to arrive at a quantitative relationship between the length of light cycle (ranging from 23 h to 30 h) and the parameters of egg quality. Eggshell quality (whether measured as mg shell per unit surface area, as shell thickness or as shell weight per se) was found to depend on a curvilinear function of cycle length. Albumen height was negatively correlated with cycle length, whereas yolk and albumen weights were found to have a curvilinear relationship with cycle length.