Archived - Shell Egg Manual - Chapter 18 – Technical Information

Table of Contents

• 18.1 Objective of Activity
• 18.2 References
• 18.3 Required Equipment
• 18.4 Required Forms
• 18.5 Structure of the Egg
  • 18.5.1 The Yolk
  • 18.5.2 The Albumen
  • 18.5.3 The Shell Egg Membrane
  • 18.5.4 The Shell
  • 18.5.5 The Air Cell
• 18.6 Microbiology of Eggs
  • 18.6.1 Contamination via shell pores (Trans–shell contamination)
  • 18.6.2 Trans–ovarian contamination
• 18.7 Yolk Colour
• 18.8 Oiling of Eggs
• 18.9 Factors Affecting Quality of Eggs
  • 18.9.1 The Shell
  • 18.9.2 The Albumen
  • 18.9.3 The Yolk
• 18.10 Guidelines for Egg Washers
  • 18.10.1 Pre–Washing
  • 18.10.2 Washing
    • 18.10.2.1 Operational Guidelines Pre–Washing
    • 18.10.2.2 Pre–wash
    • 18.10.2.3 Wash
    • 18.10.2.4 Final rinse
  • 18.10.3 Clean–up of the Washer
    • 18.10.3.1 Daily Schedule
    • 18.10.3.2 Weekly or Bi–weekly Clean–up (Acid Bath)
• 18.11 Post wash Handling of Equipment and the Eggs
  • 18.11.1 Clean–up of Packing and Surrounding Areas
• 18.12 Rodents and Insect Control
• 18.13 Temperature Conversion Table

18.1 Objective of Activity

This section of the manual provides technical information that will help in the understanding of the industry and product which the inspection programs are in place to regulate.

18.2 References

Egg and Egg Products. Publication no. 1498. Agriculture Canada. 1973

Microbial Ecology of Foods. Volumes 1 & 2. International Commission on microbial Specifications for food.  Academic Press. 1980.

Egg Science and Technology. Fourth Edition. W. Stadelman & O. Cotterill. Avi Publishing Co., Inc.

18.3 Required Equipment

Shell Egg Inspection Manual

18.4 Required Forms

Not applicable

18.5 Structure of the Egg

Before discussing the interior and exterior factors which will affect the grade of the egg, it is important to understand the structure of an egg and how it relates back to the various quality factors.

The parts of the egg are shown in Fig. 1. The egg is comprised of four main parts: yolk, egg white or albumen, shell membranes and the shell.

Albumen
1. Outer thin
2. Firm
3. Chalaze

Shell
4. Cuticle

Yolk
5. Germinal disc (blasdoderm
6. Yolk (vitelline) membrane

Membrane
7. Air cell

18.5.1 The Yolk

The yolk is formed during the final 10 to 12 days prior to the laying of the egg. The yolk consists of alternate layers of dark and light colored yolk material, latebrae, germinal disk, and the transparent vitelline membrane (yolk membrane). The color of the yolk may vary from a pale yellow to deep orange depending on the feed and individual characteristics of the hen. The germinal disk, in an infertile egg, appears as a small irregular shaped light coloured spot on the surface of the egg. The yolk is anchored within the albumen by thick white twisted cords of albumen known as the chalazae. The yolk comprises 30 to 33% of the total egg weight

18.5.2 The Albumen

The albumen portion of the egg is formed in a manner of a few hours as the yolk passes down the oviduct.  It makes up approximately 60% of the total egg weight. The albumen consists of four fractions: the chalaziferous layer, the inner thin layer, the structural or firm gel–like layer and the outer thin layer.

18.5.3 The Shell Egg Membrane

The inner and outer shell membranes each consist of two or three layers of unorganized, interwoven protein fibers. The two membranes serve as one of the eggs chief defenses against bacterial invasion. The membranes however are not impervious to either gasses or micro–organisms because of the presence of fine pores.

18.5.4 The Shell

The outer covering of the egg, the shell, comprises 9 to 12% of the total egg weight. The shell itself is composed of about 94% calcium carbonate, 1% magnesium carbonate, 1% calcium phosphate, and 4% organic matter, chiefly protein. The shell is formed in a distinct pattern with pores for gas exchange. The pores are partially sealed by the protein (Keratin), but do allow the loss of carbon dioxide and moisture from the egg. Bacterial penetration is also possible through the pores. The protein covering the shell is called the cuticle or bloom.

18.5.5 The Air Cell

There is no air cell in an egg at the moment it is laid. The contents completely fill the shell. As the egg cools, the internal contents contract and air is drawn through the porous shell to form an air space between the two shell membranes. The air cell normally forms at the large end because the shell is more porous at that end. As the egg ages, it will lose moisture through the pores in the shell and consequently, the air cell will grow larger.

18.6 Microbiology of Eggs

Eggs are one of the most nutritionally complete foods there are. It supplies all of the nutrients essential for the complete development a chick. For humans it is one of the most digestible foods there is and is second only to breast milk in its nutritive value. Unfortunately, it also provides an excellent source of nourishment for microorganisms.

At the time of laying, the egg is usually clean and contains very few bacteria on the surface of the shell.

If an egg becomes contaminated, bacteria can grow very quickly given the right conditions. This can result in spoilage of the egg. Certain types of bacteria, such as Salmonella, can cause illness in humans and, in severe cases, can contribute to the death of an infected individual.

There are two ways eggs can become contaminated. One is through the pores in the shell (trans–shell contamination) and the other is transmitted into the egg by the chicken before the shell is formed (trans–ovarian contamination).

18.6.1 Contamination via shell pores (Trans–shell contamination)

The most obvious way an egg can become contaminated is if the shell and membrane are broken. This is classified as a leaker and is not fit for human consumption. Eggs that are cracked, with the membrane remaining intact, are considered a high risk. These eggs should only go to a processed egg station where they will be broken and then pasteurized to destroy any pathogens that may be present.

Even if the shell is intact, bacteria can still pass through the pores in the shell and penetrate the membrane. This contamination can result in a number of ways.

• The first is washing the eggs in water that is too cold. This can cause the contents of the egg to contract and the resulting pressure differential will result in contaminated water being drawn into the egg. Wash water must be 11°C warmer than the egg to prevent the pressure differential from occurring.
• Packing eggs that are not dry can also lead to bacteria entering the egg. The presence of water on the shell facilitates the passage of bacteria through the pores of the shell. When the graded eggs are moved to the cooler, the cooling of the egg will cause the contents to contract. If there is excess water on the shell, it can be drawn into the egg possibly resulting in contamination of the egg.
• Similarly, eggs that sweat as a result of moving from a cooler to a room with high humidity can also lead to contamination.
• Dirt on the shell (i.e. manure and yolk from leakers) is likely to harbour microorganisms which may pass through the pores and contaminate the egg's contents.

The egg does have a final line of defense to prevent contamination. There is are antibacterial enzymes (lysozyme and conalbumin) in the albumen that will inhibit the growth of bacteria for a time. Some organisms, like Pseudomonas fluorescens, compete with the conalbumin for iron and may have particular properties which allow them to grow more easily in the egg and cause spoilage.

18.6.2 Trans–ovarian contamination

This type of contamination occurs through the hen herself. If the hen harbors Salmonella enteriditis (S.e.) she can pass this to the egg. Particular types of S.e. have been responsible for some very serious outbreaks in humans and many people have been hospitalized as a result. If a flock is identified as a carrier the eggs must be sent to a registered processed egg station to be pasteurized and the flock is then destroyed. New birds are not placed on the farm until a thorough cleaning is undertaken and the barn is free from S.e.

Research has shown that the growth of S.e. can be inhibited if kept under proper refrigeration.

18.7 Yolk Colour

The colour of the yolk is almost completely dependent on the feed the hen eats. The colour is closely associated with the carotenoid pigments (mainly xanthophyll) in the diet. The two most commonly used feed ingredients that are responsible for most of the colour in egg yolks are corn and dehydrated green feed. Rations containing a high present of either of the above will have a dark yolk colour. A ration containing only wheat as the cereal grain would be much lighter (a pale yellow).

A Roche Yolk Colour Fan provides a simple means of measuring yolk colour. The method consists of a comparison of the yolk under test areas on a colour–scale shaped like a fan. The scale covers the entire range of natural yolk colours (pale greenish yellow to deep orange).

18.8 Oiling of Eggs

The advantages of oiling on the farm are that when eggs are laid, they are relatively clean and contain a cuticle. If these eggs are oiled within the first 10 to 12 hours after lay, the oiling will have a sealing effect on the pores of the shell and help maintain the interior quality of the egg. It will also provide a protective coating and would inhibit the entrance of bacteria into the pores. The oil also has a loosening effect on the dirt to facilitate later removal. Oiling of eggs at the grading station is normally practised after the washing of the eggs. This kind of application is potentially dangerous, particularly if the wash water is contaminated. Rule of thumb for oiling eggs: oil clean and dry eggs only.

18.9 Factors Affecting Quality of Eggs

Note:  The information in these tables is not intended for use as a diagnostic tool. It is intended to give the reader an awareness of the possible causes of quality problems. It is not intended to be used as a tool to correct problems. That is the role of trained specialists in this field.

18.9.1 The Shell

18.9.2 The Albumen

18.9.3 The Yolk

*The information in this table was obtained from F.E. Cunningham, Kansas State University.

18.10 Guidelines for Egg Washers

This section is intended to give the inspector an understanding of how eggs should be washed. It is a guideline and could be an aid to identifying problems.

18.10.1 Pre–Washing

It is important that the grading station have a good idea of the amount of stain, the amount of dirt, the number of weak shells and the extent of leakers in the pack of eggs prior to washing. Where excessive numbers of any of these kinds of eggs exist, extra effort must be made to remove these eggs prior to the washing stage. This can be accomplished by placing personnel prior to the washer to remove these types of undesirable eggs. Lots of eggs that are in bad condition should be washed at the end of the shift to prevent contaminating the wash water.

18.10.2 Washing

18.10.2.1 Operational Guidelines

• Shell temperature is usually around 7–13°C (45–55°F). Pre–rinse 32–35°C (90–95°F).
• This pre–rinse can have a warming effect on eggs as well as a pre–soaking for eggs with dirt. The warming effect of the pre–rinse stage is important, particularly when cool eggs are received at the washer, such as at 7°C (45°F) or less. The pre–rinse will warm the shell in an effort to eliminate thermal cracks prior to the entrance into the washer. In addition, the soaking effect will facilitate the removal of dirts during the washing process.
• Many wash water temperatures have been tried and are used, however the most popular wash water temperature, that of approximately 43–46°C (110–115°F), will have little effect on eggs received at 13°C (55°F) and will aid in the effectiveness of the detergents.
• The final rinse is used primarily to remove detergent and wash water from the shell and to have a warming effect on the shell in preparation for the blower and the final drying of the eggs. Recommended temperature here is from 49.0–54.4°C (120–130°F).
• The Air Blower – The purpose of the air blower is to aid in the drying of the eggs. The lower the relative humidity the better, since a low relative humidity aids in drying the water from the surface of the egg shell. A relative humidity of less than 85% is recommended. The temperature of air from the blower can range from 20–24°C (68–75°F) depending on room temperature or the temperature of outside air. The filter on the intake must be kept clean.
• Dry Eggs – For the purpose of minimizing bacterial counts on the shells of eggs and to reduce the possible contamination of the eggs during cooling, every effort should be made to dry the eggs prior to packing.

Caution: A temperature difference between the wash water and the egg should never be greater than 28°C (50°F) to minimize the likelihood of causing thermal cracks. However the wash water temperature should always be at least 11°C (20°F) warmer than the shell in order to discourage the entrance of wash water into the pores of the egg.

18.10.2.2 Pre–wash

The pre–wash need only be a water spray to have a warming effect on cold eggs and a moistening effect to aid in the removal of dirt during the washing procedure.

18.10.2.3 Wash

Maintenance of the washers and parts of the washers is very important for the effective and efficient washing of eggs.

• Brushes should be properly adjusted according to the manufacturer's guidelines. When brushes become worn they should be replaced. Brushes should not apply an excessive amount of pressure on the eggs.
• Spray effectiveness depends on:
  • Good repair of the nozzles, all should be working;
  • Advantageous to have direct spray through the brushes onto the egg where possible;
  • Rollers should be in good working order;
  • A screen should be in place to cover the reservoir opening.
• The exhaust must be directed to the outside, and be capable of removing all of the steam and moisture coming from the washer. The exhaust can become very dirty and a possible source of contamination. There should be an inspection port on the exhaust so that the cleanliness of the exhaust can be verified and that there is no condensation dripping back onto the eggs.
• Effective results have been achieved by maintaining a continuous change of water. This can be achieved by allowing a significant amount of water to continually drain from the machine while new water is being added.

Some of the changes made to conventional washers which have been beneficial are:

• An input of water at the bottom of the reservoir. The purpose of this is to have a better cleaning effect during the clean–up period. The water is flushed along the bottom of the tank, aiding in the removal of particles settling there.
• Varying degrees of continuous draining and overflows have been tried. This continuous draining and overflow is beneficial only if frequent changes to the wash water have occurred, that is approximately every two hours.
• In the case of those reservoirs which contain heating coils, these coils should be raised for cleaning purposes. Note: A system that has been tried in an aid to clean the coils is to turn them on for a brief period of time when the reservoir is empty. This should be monitored carefully, and the coils left on just long enough to cook off the adhering material.

Organic and inorganic (including hard water) materials cause dirty wash water. These materials bind detergents and inhibit their activities. Organic and inorganic compounds act as elements for the growth of bacteria. Hard water in itself can cause excessive scaling on the equipment. Many egg stations have switched to soft water to reduce scaling/foaming effect in the water. As the pH increases to 11, to 12 to 12.5, there is a bactericidal effect on gram–positive bacteria. In addition, a higher pH for a short period of time may be used in wash water having high bacterial counts. This method still needs to be proven, and further data collected as to the effects of this pH shock treatment of the water, on equipment and the shell of the egg.

Primarily two kinds of detergents are used in the egg industry: the chlorine base and the non–chlorine base. Either can be effective if used under proper conditions.

The metering of detergents into the wash water has many advantages. Most importantly, it supplies a constant level of detergent in the water for the cleansing action on the eggs. It also tends to maintain a constant pH level in the water, particularly when trying to maintain high pH levels to prevent bacterial growth.

Intermittent use is a procedure where detergents are added in batch amounts as recommended by the manufacture at various intervals of the washing cycle. The disadvantage of the approach is converse to the metering approach in that we have a tendency to have uneven levels of detergent in the wash water, resulting in fluctuating pH levels.

18.10.2.4 Final rinse

Final rinses are primarily used to wash the detergent from the egg and raise the temperature of the shell to facilitate drying. For the most part, plain water rinses are used.  There are conflicting evidence on the use of sanitizers in these rinses. One of the strong advantages of using a chlorine sanitizer from a microbiological point of view is the residual effect of the sanitizer on the equipment surfaces which come in contact with the egg. The final rinse may be diverted to the reservoir to add to the incoming fresh water into the reservoir.

18.10.3 Clean–up of the Washer

18.10.3.1 Daily Schedule

A pre–rinse prior to start–up would be optional depending on the performance of the machine. If low bacterial counts are being achieved, the pre–rinse may not be required. During the day's operation, if the tank is drained, it should be sprayed during the draining process with a high–pressure water spray to remove particles from the inside of the washer. The screens covering the reservoir should be cleaned and scraped every two hours or more often if required.

At the end of the day, the tank should be drained completely, and the lid left open. Using a high pressure water spray (150–200 lbs per sq. ft), thoroughly spray the inside of the washer and reservoir tank. The temperature of the water used for rinsing should be 49–55°C (120–130°F).

Next, ensure that the brushes are sprayed clean, as this is one of the more troublesome areas for product and bacteria build–up. Scrape the screens thoroughly. Use scrub brushes on those areas that have not been properly cleaned. The use of detergent is recommended. It is felt; however, that detergent use may become optional where good cleaning schedules have been maintained. When detergents are used in conjunction with the pressure spray, a rinse will be required to remove the detergent from the walls of the washer. Drain the washer, and leave the lids open to ensure that they are dry. Drying of all areas of the washer is one of the important factors in maintaining low bacterial counts.

18.10.3.2 Weekly or Bi–weekly Clean–up (Acid Bath)

Perform the daily routine. Fill the tank with water, preferably between 43–66°C (110–150°F). Add the acid cleaner as per the manufacture=s recommendations. Circulate the water through the washer for approximately one hour. Drain the acid solution. Rinse the tank with the high–pressure water spray and let dry. The use of warm water in conjunction with this wash will aid the effects of the acid as well as facilitate faster drying after the rinse.

18.11 Post wash Handling of Equipment and the Eggs

All equipment, including the conveyors, washer, dryer, candling booth, scales and packer should be kept clean and in good repair, following manufacturer's recommendations. The glass protector over the candlers should be clean to prohibit any bacteria build–up in this heated area. A screening filter should be used to prohibit the entry of heavy dust or dirt particles into the blower. Towels used for keeping conveyor belts clean must be washable or disposable, and should be changed once a day or more often if necessary. Caution should be taken during cleaning to avoid damaging any equipment components, especially when electronic parts are involved.

18.11.1 Clean–up of Packing and Surrounding Areas

The floor and area around the washer and packers should be cleaned at least once a day, and more often if excessive spillage occurs. These areas as well as the non–contact surfaces of the equipment should be cleaned periodically to avoid the build–up of egg meat or dirt.

18.12 Rodents and Insect Control

Satisfactory plant construction in keeping with an excellent housekeeping program, along with the use of screens, air curtains, and electrical insect control devices are the first steps in avoiding the introduction of insects and rodents. Vermin, through their habits, are capable of introducing serious human diseases to food products.

Insecticides and rodenticides, when properly handled and utilized, serve as useful aid in eradication and control of vermin. This use however must not be a substitute for satisfactory plant construction or an effective housekeeping program.

The responsibility for the safe use of the products rests with plant management. Only licensed pest control operators or designated trained plant employees should be involved with the preparation and application of these products. All personnel, including inspection staff, should understand and appreciate the potential hazard these materials represent to both food products and the health of personnel in the plant.

Insecticides may be residual or non–residual. In food processing plants, sprays may only be used when the plant is not in operation. No exposed food products, ingredients or packaging material may be left in the room and all food equipment should be covered. All surfaces that may come into contact with food products should be thoroughly washed and rinsed with potable water after the spray treatment.

Rodenticides are sold in dry or liquid form and used in a variety of types of bait stations. Bait stations are only permitted to be used outside, but if used, they must be of the covered variety and are to be adequately serviced. All bait stations must be clearly identified and a map of their locations given to the inspection staff.

Plant management must demonstrate that all insecticides and rodenticides in the plant are being stored and used in accordance with the instructions on the label and that edible products are not being placed at risk because of the presence of these pesticides.

A list of all registered pesticides can be found on Health Canada's Pesticides and Pest Management website, or information can be obtained through contacting your local Health Canada staff.

18.13 Temperature Conversion Table