HOW TO STORE EGGS

PRESERVATION TECHNIQUES TO STORE EGGS

A freshly laid egg has the best quality at the time of production. Since egg is full of essential nutrients, deteriorative changes soon start taking place which may pose danger to the quality of egg. The process of maintaining the quality of eggs by employing various methods is known as preservation of eggs.

All preservative methods for shell eggs have been designed to retard one or more of the following physico-chemical alterations which lower the quality of stored egg as it ages:

1. As the egg surface dries, the cuticle shrinks and size of shell pores increases rendering it easier for gases and microorganisms to pass in and out of shell.
2. As the warm egg cools down, the egg contents also contract resulting in formation of air cell.
3. The breakdown of carbonic acid causing loss of CO₂ from the albumen is rapid during the first few hours after the egg is laid. The alkaline pH acts on the mucous fibres to disturb the thick gel of albumen making it thin or watery.
4. As the egg ages, water migrates from the albumen to the yolk which may over stretch, weaken or even rupture the vitelline membrane.
5. High temperature, improper humidity and unsanitary condition also lead to deterioration of the quality of egg.

It is essential that only clean fresh eggs with sound shell and high quality should be selected for preservation. The various preservation methods of eggs employed are:

1. EGG CLEANING
2. OIL TREATMENT
3. COLD STORAGE
4. THERMOSTABILIZATION
5. IMMERSION IN LIQUIDS

1. EGG CLEANING: The degree of cleanliness is largely dependent on the production practices followed at the farm. As consumer’s first attention is directed towards cleanliness of eggs; therefore, a number of techniques have been developed to improve its cleanliness. However, only dirty eggs should be cleaned and they should be disposed off quickly.

• Dry Cleaning: Usually followed when eggs are slightly soiled.
  • Hand buffing: Done by hand with an abrasive material.
  • Machine buffing: In this, abrasives are put on mechanically rotating wheels so that individual egg could be cleaned rapidly by holding against abrasives.
  • Sand blasting: This is done with the help of sand particles which beat against the shell surface.

Disadvantages: Although soil marks are reduced largely but at the same time it takes away also the shell material resulting in shell weakness. Sometimes, abrasive marks appear on egg shell.

• Wet Cleaning (Disinfection): Washing of eggs in warm water containing detergent/sanitizer is an effective way of cleaning the eggs with dirty shells. Unless precautions are taken, wash water will build up number of spoilage bacteria rather than reducing the load. The temperature of water used for washing eggs ranges from 32.3 – 60^oC, depending upon chemicals employed. Chemicals used for washing eggs include hypochlorite, acetic acid, quaternary ammonium compounds, formalin, detergents, etc. The temperature of wash water should be about 10-15^oC higher than the temperature of egg as the difference of more than this increases the number of cracks in eggshell due to expansion of egg contents. Eggs should be immersed in the warm water for not more than 4 minutes.

Preservation of shell soundness can be achieved by:

• Gentle handling of eggs.
• Proper filling of egg baskets.
• Use of right type of egg carton and packaging materials.
• Proper transportation methods.

2. OIL TREATMENT: Coating/spraying of different oils on egg shell is commonly done to retard the physical and chemical changes in the egg. The oil used for treatment of eggs as a coating material or spray should be odorless, colorless, free from any fluorescent material and conform to food  grade specifications. It should be done within few hours of production as loss of CO₂ is more during first few hours and moisture loss is maximum within first few days. Appreciable benefits of egg coating can only be derived if it is done within few hours. Preferably it should be done just one hour after production. Oil coating of egg is not at all useful if done after 4 days of production. Coating of eggs with oils also increases the storage life of egg in cold storage. Oil sprays are used in filler flats with broad end of eggs up. Ideal temperature of oil should be 15 to 30^oC. Vegetable oils like groundnut oil mixed with 0.0125% BHT (Butylated hydroxy toluene) is also a good sealing agent but mineral oils are preferable because they are less susceptible to oxidative changes during storage. Oil treatment safeguards quality of albumen for at least 7 days.

 3. COLD STORAGE: The treatments discussed above though effective in their own place cannot check the occurrence of other deteriorative changes brought about by high temperatures. Low temperature treatment of eggs is the most important treatment for preserving their quality. The important factors to be looked into during cold storage of eggs are the maintenance of proper temperature, humidity and sanitation in the cold storage. The cold storage can be done either by chilling or by freezing.

    a) Chilling: Most shell eggs are preserved by chilling. The eggs should be cooled as promptly as possible after production. Selection of temperature and relative humidity while chilling depends upon anticipated time of storage. For commercial storage for 6 months or longer, a temperature of -1.7 to 0.55 ^oC and a relative humidity of 70-80% are recommended. For short period (few days) of storage, store fresh eggs at 12.5 – 13.5 ^oC at 70-80% relative humidity.

Advantages:

• Cold temperatures retard the loss of CO₂ through shell since gases are more soluble in  cold liquid than warm one.
• Less evaporation takes place at lower temperature.
• The flow of water from the albumen through the vitelline membrane is retarded.

            Impregnation of eggshell with colorless and odorless mineral oil while chill storage further keeps out moisture, slows desiccation and air penetration, retains CO₂ and also retards physical and chemical changes.

    b) Freezing: Freezing keeps eggs longer than any other method even up to one year at 0^oF (-18^oC). Freeze only raw eggs because cooked eggs will turn rubbery. Since, eggs that are frozen intact will expand and burst their shells. The shell must thus be removed before freezing. Thaw frozen eggs overnight in the refrigerator or in air tight container placed in cool water at 10-16^oC before use. Thaw only as many eggs as you will use within 3 days.

4. THERMOSTABILIZATION: It aims at coagulating the thin albumen immediately beneath the shell membrane, which acts as a moisture and gas barrier. It is better than oil coating technique but both the techniques are complimentary to each other. It can be achieved by immersing the eggs for 15 minutes in an oil bath at 55 ^oC or for 8-10 minutes at 58 ^oC. Alternatively, immersion in hot water at 71^oC for 2 to 3 seconds called as Flash heat treatment can be done. Bacteria on shell get killed and thin albumen coagulates.

5. IMMERSION IN LIQUIDS: This can be achieved by:

    a) Immersion in lime water: The treatment deposits a thin film of calcium on the shell and partially seals the pores. Eggs can be stored for 3-4 weeks at room temperature.

    b) Immersion in Water Glass: This deposits a thin precipitate of silica on the egg shell. It possesses intrinsic antiseptic property and does not impart any foreign odor or taste to eggs.

PROCEDURE OF PRESERVATION METHODS

Requirements:

Heating device, wire basket, thermometer, cold storage facility, mineral oil, sodium chloride, calcium oxide (quick lime), sodium silicate (water glass)

Methods:

Oil treatment:

1. Dip the eggs in good mineral oil (15-30^oC) or coat mineral oil on the eggs. Alternatively spray any mineral oil on the shell surfaces of eggs placed on the trays.
2. Pack the eggs in suitable packaging material and store.

Thermostabilization:

1. Take oil/water in a suitable container and heat with the help of a heating device.
2. Using a thermometer, check the temperature of the oil/water.
3. Immersing the eggs for 15 minutes in an oil bath at 55^oC or for 8-10 minutes at 58^oC.
4. Alternatively, immersion in hot water at 71^oC for 2 to 3 seconds (Flash heat treatment) can also be done.
5. Store the eggs in a suitable packaging material.

Cold storage:

1. For short period of storage, store fresh eggs at 12.5 – 13.5^oC at 70-80% relative humidity.
2. For commercial storage for 6 months or longer, a temperature of -1.7 to 0.55 ^oC and a relative humidity of 70-80% are recommended.

Immersion in liquids:

1. Immersion in lime water

1. Boil 1 litre of water.
2. Add 1 kg of quick lime to it.
3. Bring the solution to room temperature
4. Add 5 litre of cold water and 225 g of sodium chloride. Allow to settle down.
5. In the clear fluid, immerse eggs for 16-18 h.
6. Take the eggs out and store at suitable temperatures.

2. Immersion in glass water

1. Prepare water glass by diluting 1 part of sodium silicate with 10 parts of water.
2. Leave the eggs immersed in the solution overnight.
3. Take the eggs out and store at suitable temperatures.