The ancient Chinese stored eggs up to several years by immersion in a variety of imaginative mixture as salt and wet clay; cooked rice, salt and lime; or salt and wood ashes. Eggs are classified under ‘most perishable’ commodity. The rate of spoilage is very rapid when the eggs are opened out because of high nutritive value of contents acting as an excellent medium for growth of microorganism.

Generally, eggs can be preserved; with shell or their contents may be preserved by various methods. Preservation of shell-egg is primarily aimed at maintaining the interior quality rather than minimizing the microbial spoilage.

In wet method, eggs come in contact with a solution usually prepared with water as solvent. Most of the shell-pores will be blocked during the process and hence a small pin hole has to be made before boiling the eggs stored by wet methods to avoid breakage of shell.

Lime water method is one such method where one kilogram of quicklime is mixed with one litre of water and allowed to react. After the reaction is over, 120g of salt is added to increase the specific gravity so that none of the eggs touches the bottom of container when immersed. Then five to six litres of water is added and stirred thoroughly and filtered through a muslin cloth before a small quantity of slaked lime added to maintain concentration. The eggs are then held in the solution for 14 to 16 hours. Later on they are removed and can be stored at room temperature for future use.

In water glass method a 10% solution of sodium silicate, popularly known as ‘water-glass’, a bacterial resistant solution discourage the entrance of spoilage organism and evaporation of water from eggs. In this method eggs can be stored in a cool place up to 8-9 months. Water glass is a colloidal solution and hence, sodium silicate molecules absorb the shell surface and physically block the effective shell pores.

In this method water is boiled thoroughly to remove the dissolved carbon dioxide which forms a complex with sodium silicate added to the solution in required amount. Eggs are then dipped in the cooled water glass solution and kept overnight before being taken out and stored at room temperature for future use.

In dry method eggs do not come in contact with water. For this method oil and gas are used or simply the cold storage procedure is resorted to to preserve eggs. In oil method, an attempt is made to seal the pores to prevent loss of moisture and carbon dioxide using a variety of minerals, including cactus juice, soap, minerals oil (byproduct of petroleum industry), etc. Bactericides and fungicides are added to the oil to enhance efficacy.

In gas method inert gases are used to preserve eggs. Eggs are kept in plastic bags which are filled with gas and then sealed. Usually nitrogen and carbo dioxide in a ratio of 94:6 is used for this method. Higher carbon dioxide pressure outside the eggs precludes its loss from inside the eggs, thus affording protection to egg quality.

Cold storage of eggs is done at 10-15.60C and a relative humidity of 75-90%. Air circulation is also important to effect a proper loss of heat from eggs. It should be kept in mind that freezing point of albumen is –0.420C while that of yolk is –0.650C and that the albumen yolk is –2.220C. Eggs can be kept for a long time (up to 8-10 months) in cold storage.

These are the common and effective methods for preservation of eggs. The spoiling of eggs is due to the entrance of air carrying germs through the shells. Normally, the shell has a surface coating of mucilaginous matter, which prevents for a time the entrance of these harmful organisms into the egg. But if this coating is removed or softened by washing or otherwise, the keeping quality of the egg is reduced. These facts explain why many methods of preservation have not been entirely successful, and suggest that the methods employed should be based upon the idea of protecting and rendering more effective the natural coating of the egg shell, so that air bearing the germs that cause decomposition may be completely excluded.

Dhirashree Choudhury