E g g Q u a l i t y G u i d e

Introduction 3

Section 1

1 The Structure of the Egg 4

2 Egg Formation 6

3 Common Internal and Egg Shell Faults 9

4 Composition and Nutrient Content of Eggs 14

5 Effects of Storage Upon Egg Quality 16

Section 21 Grading of Eggs For Human Consumption 17

2 Quality Standards – The EU Egg Marketing

Regulations and Other Controls 17

3 Quality Control Methods for Eggs 20

Section 3Glossary of Terms 26

Section 4Pictorial Guide to Egg Quality 28

2

C o n t e n t s

3

The egg was never intended to be eaten, yet it has been used in

human diets since early times. There is evidence that wild birds

eggs were included in the diets of primitive peoples long before

the development of agriculture.

To d a y, eggs remain a staple food within the human diet, consumed

by people throughout the world. They are recognised by consumers

as versatile and wholesome and they have a natural balance of

essential nutrients.

H o w e v e r, eggs have to compete for sales with an increasing number

of other products in the modern food industry and to compete

successfully they have to overcome certain disadvantages. For

example, they are fragile and they deteriorate in quality with age.

Furthermore, each of the main components of the egg (the shell,

the albumen and the yolk) has a natural variability which is not in

keeping with the modern consumers requirement for consistency.

Planned production methods and efficient quality control proce-

dures help to reduce this variation and are fundamental to the

successful marketing of eggs. All those involved in production,

grading and packing must be aware of the defects which can

occur in eggs, the likely causes and the means of identifying and

removing those which are unsuitable.

It is hoped that this book will be of relevance and interest to all

those involved in the production and marketing of eggs for

human consumption. In Section 1, information is presented on

the structure, formation and nutrient content of the egg and on

the causes of common quality faults. Section 2 summarises

current legislation and provides a guide to quality control

methods for those involved in pre-candling and candling

inspection of eggs. Definitions of some of the technical terms

used are given in Section 3 whilst Section 4 contains a pictorial

guide to egg quality.

I n t r o d u c t i o n

I n t r o d u c t i o n

1 The st ructure o f the egg

4

An egg consists of a yolk at the centre, surrounded by albumen(white), both of which are enclosed within the shell. However,the detailed structure of an egg is more complex than it firstappears as the diagram at Figure 1 shows.

The YolkThe yolk consists of fats, vitamins and minerals, together withabout half of the egg’s total protein content. A transparent barriercalled the vitalline membrane surrounds the yolk and preventsthe yolk contents leaking into the albumen. Inside the yolk is thegerm cell (or germinal disc). This is the site of cell division if theegg is fertile. The colour of the yolk varies and it is influencedby the laying hen’s diet. The colour of the yolk has noconnection with food value.

The AlbumenEgg albumen is rich in protein and vitamins and it containssubstances which protect the egg from micro-organisms whichmay have entered through the shell. In a freshly laid, goodquality egg, alternating layers of thick and thin albumen areclearly visible.

The innermost layer of thick albumen (the chalaziferous layer) isextended at two points, forming the white, fibrous chalazae

Fig 1 The structureof an egg

5

which are anchored in the outer thick albumen. The structure ofthe albumen is designed to provide support and protection tothe yolk, holding it centrally inside the egg.

The Egg ShellThe egg shell consists of the inner and outer shell membranes,the true shell and the cuticle. In total it is approximately onethird of a millimetre thick and over 90% of it is made of calciumcarbonate. There are also small quantities of proteins and otherminerals.

Several thousand tiny porespermeate the shell, the majority ofthem are usually at the broad end ofthe egg. The pores allow gases tomove between the contents of theegg and the surroundings.

The diagram in Figure 2 shows atransverse section through anegg shell.

The two shell membranes have a dense structure which inhibitsthe movement of micro-organisms into the egg. They also actas a foundation, providing a solid base upon which the trueshell is built.

The true shell is built in columns of calcium carbonate fromindividual ‘seeding sites’ on the membranes. When completed,the shell is rigid but brittle. Shell strength is determined not onlyby shell thickness but also by shape and structure.

The outermost part of the shell is the cuticle which gives the eggits characteristic bloom or shine. When the egg is laid, thecuticle is still moist although it will dry within a minute or two.The cuticle normally covers the pores and this provides extramicrobiological protection, especially when the egg is fresh.

Sect ion 0ne

Fig 2 Transverse sectionthrough an egg shell

The formation of an egg can be compared to an assembly line ina factory. A number of component parts are needed and these mustbe assembled in the correct order and quantity. If the process isdisturbed or becomes de-synchronised, faults will occur.

Egg formation and development occurs in the ovary (where theyolk develops) and the tube-like oviduct which acts as theassembly line. Most female animals have two active ovaries andoviducts but in the hen, only the left ovary and oviduct isfunctional. The right ovary and oviduct remain dormant.

Figure 3 shows a representation of a mature ovary and oviductfrom a laying hen.

Yolk DevelopmentIn the ovary, the yolk develops from a minute ovum. A femalechick is born with a miniature version of the fully formed ovarybut this hardly changes in size during the growing stage.

When the hen reaches maturity, the ovary begins to increase insize. Each ovum (the future yolk) begins to develop during anactive growth stage, a process which takes 7-10 days in all.

The developing yolks are enclosed in a sac or follicle. They arespherical in shape and each one is attached by a stem to the

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2 Egg formation

Fig 3 The hen’sreproductive system

7

ovary wall, so that the whole structure looks like a bunch ofgrapes. The sacs have an excellent blood supply which deliversessential nutrients. As each yolk grows, its colour changes frompale grey to a characteristic yellow.

Ovulation and Egg LayingWhen the yolk reaches its final size, it breaks away from theovary. This process is called ovulation. The yolk enters theoviduct (see opposite) where the albumen and the shell areadded. The process from ovulation to egg laying takes around24-26 hours.

Shortly after an egg is laid, ovulation takes place again. Anotheryolk is released into the oviduct and the process which will leadto the next day’s egg begins again. The interval between thelaying of one egg and the ovulation of the next is approximately30 minutes. The timing of egg laying gets gradually later eachday. Hens in full production will lay an egg each day for severaldays and this group of eggs is known as a clutch. Each clutch isfollowed by a sequence of one or more days when the bird doesnot produce an egg.

Sect ion One

The parts of the oviductThe oviduct is like a coiled tube which, if straightened, wouldbe 60-80 cm in length. It extends from the ovary to the cloacaand varies in diameter along its length. It can be divided intofive distinct parts.

1 The Infundibulum (Funnel)The infundibulum is the entrance to the oviduct, where theyolk is captured after ovulation. It begins in a funnel shape,some 9cm in diameter but narrows quickly. In a hatching egg,it is the site where fertilisation takes place. The yolk takesaround 15 minutes to pass through this area.

2 The MagnumThe magnum is the longest section of the oviduct and theegg takes some 3 hours to pass through. It is here that thealbumen is added. The egg rotates, so producing andstretching the chalazae. The albumen is laid down in circlesaround the yolk.

3 The IsthmusThe addition of albumen is completed and the shell membranesare formed in the isthmus, a process taking around 1-11⁄4 h o u r s .

4 The Shell GlandThe shell gland area consists of the tubular shell gland and theshell gland pouch. As the egg moves through, a waterysecretion is added to the albumen. Gradually, this plumps upthe egg until the shell membranes become stretched. Thisprovides a firm base on which the true shell can form. Theshell formation process takes just over 20 hours and finisheswith the addition of pigment and cuticle which give the shellits colour and bloom.

5 The CloacaThe egg is released through the cloaca or vent. The muscles inthe uterus contract and invert. The egg is pushed out, usuallybroad end first.

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9

Many different factors can disturb the egg formation process andthese in turn can increase the incidence of second quality eggs.

Eggs can also be damaged after they are laid, either by crackingor by contamination. Some typical internal and external faultsand abnormalities are listed below together with their likelycauses.

Internal Egg Quality Faults & Abnormalities

Double Yolked EggsIn a young, highly productive laying hen, two yolk ovulationsmay take place almost at the same time. When this happens, thetwo yolks progress as one down the oviduct in juxtaposition andthey enter the shell gland together.

Blood Spots in EggsThese are normally found in or around the yolk. They can becaused by one of the tiny blood vessels in the ovary breaking atthe time when the yolk is released. High levels of activity ordisturbance, particularly at the time of ovulation are likely toincrease the incidence of these.

Eggs from free range laying hens may have some protection fromblood spots due to rutin, a substance in the grass which hassome effect in stopping bleeding.

Meat Spots in EggsMeat spots are usually brown in colour and associated with thealbumen rather than the yolk. They often consist of small piecesof body tissue, such as the internal wall of the oviduct. Theirincidence varies according to bird age and health and also dueto strain (breed) differences. In brown shelled eggs, they aremore difficult to identify without breaking the shell and there isalso evidence that brown laying hens are more likely to producethem than white hens.

Watery WhitesThe internal quality of freshly laid eggs deteriorates withincreasing flock age and some eggs from older birds may haveunacceptably watery whites even when laid. Viral diseases such

Sect ion One

3 Common interna l &e g g s h e l l f a u l t s

Double yolked egg

as infectious bronchitis can also affect the ability of the bird toproduce thick albumen.

Abnormal Yolk ColourThe colour of the yolk is determined by the diet of the bird,although some disease conditions can also contribute. Greenyolks can be caused by birds consuming green herbage toexcess. The colour can vary from olive to khaki but may onlyaffect a proportion of birds within a flock. The fault occurs mostfrequently in the spring when herbage is most lush and wherebirds take a higher proportion of their feed from the range.

Mobile & Bubbly AirspacesAlthough the airspace usually forms at the broad end of the egg,it can occasionally be found where there is a shell structure faultor abnormality. In other casaes, a bubbly air space may be seenwithin the albumen and this is usually caused by a rupturedinner membrane.

Bacterial and Fungal ContaminationBacteria and moulds may naturally be present on the surface ofthe egg shell. In certain circumstances, some of these can passthrough the shell and multiply within the egg, typically producingblack, red or green rots. If such eggs are examined using acandling lamp, they will appear as dark, irregular patches.

External Egg Quality Faults

Misshaped EggsIf albumen quality is very poor, there is no sound foundationupon which to build the true shell. The result can be thedistinctive ‘crinkled’ shell typical of certain viral diseases.Misshaped eggs can also arise for other reasons. For instance,the shell may break in the shell gland during the formationprocess. The damage can be partly repaired but a bulge formsaround the centre of the egg (an equatorial bulge). Any factorwhich causes disturbance to the birds 10-14 hours before theegg is laid is likely to increase the incidence of this fault.

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Mobile airspace

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Coated ShellsAdditional calcium may be deposited onto some eggs causingcalcium splashing or a pink or lilac coloured egg. Typically thesefaults are caused by the egg remaining in the shell gland for anextended period. Often young flocks just coming into productionare very susceptible to this and any stresses or disturbances atthe time when the egg is due to be laid will encourage the birdto retain the egg.

Rough Shelled EggsIn some cases, two eggs may be in the shell gland at the sametime and this can cause a form of rough shelled egg oftenreferred to as a ‘target’ or ‘thumb-print’ type. This problem acnalso result in ‘slab-sided’ eggs. There are other types of roughshelled eggs, including those with pimples or a sandpaper-typetexture. Bird health and age often affect the incidence of this.

Pale Shelled EggsSome of the egg shells laid by brown laying hens may be verypale or white in colour. The effect is purely cosmetic but sucheggs may be rejected by certain customers. Older laying hensand disease conditions tend to increase the incidence of paleshells. There is also some evidence that pale shelled eggs aremore common in free range flocks.

Soft and Weak Shelled EggsSoft and weak shelled eggs can be common in older birds,especially those which are nearing the end of the laying period,having produced a high output of eggs.

Where they are seen in younger flocks, they can be associatedwith coated or rough shells. If an egg is retained in the shellgland for too long, the next ovulation takes place at the usualtime but before the previous egg is laid. The second egg mayspend less time than normal in the shell gland and the result isa soft or shell-less egg. In such cases, a hen may not lay an eggon one day but may lay both a coated and a soft-shelled egg onthe next.

Sect ion 0ne

As a general point, it should be noted that a single stress ordisturbance to a flock of laying hens can be enough to de-synchronise the processes of egg formation for several days. Thiscan cause a prolonged effect upon egg quality and during thistime, a number of different egg quality faults may be seen.

Inadequate nutrition can also lead to inferior egg shell quality.An egg shell contains around six grams of calcium carbonateand adequate daily supplies are needed. The laying hen has aparticular requirement for calcium at the time when the egg is inthe shell gland. If calcium supplies are not maintained, thenshells will become progressively thinner and egg productionmay decline or cease.

Temporary thinning of the egg shell may occur during periods ofhigh temperature (above around 25°C) since feed intake isreduced. The shells quickly regain normal thickness whentemperatures are reduced and feed intake increases.

Cracked EggsEgg shells can easily be damaged after the egg is laid andcracking is one of the most common reasons for downgrading. Itmay be due either to an inadequate egg shell being laid or topoor handling which may occur during collection, grading ortransportation.

Three main types of cracks are identified:

Hairline cracks are the most difficult to identify, particularly invery fresh eggs. Skilled candling is needed together with idealworking conditions. Hairline cracks are often caused by an eggcolliding with an inflexible surface.

Star cracks may often be visible under normal light althoughthey are more easily seen during candling. A central point ofimpact may be seen and star cracks are often due to collisionsbetween eggs.

Pinhole and toehole cracks can be caused either by the birdsthemselves or by any sharp protrusions which may come intocontact with the egg. There is evidence that a fault whichappears similar may occur before the egg is laid.

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Dirty and Glazed ShellsAfter the egg is laid, it can become affected with numerouscontaminants including faecal material, dust, mud and litter (innon-cage systems), blood and the contents of other eggs. Thelatter is often referred to as glazing or varnishing.

All of these lead to eggs being downgraded and high standardsof hygiene and management, coupled with appropriate dietformulation and pest control must be maintained.

Sect ion One

CompositionOn a weight basis, the egg consists of around 11% shell, 58%albumen and 31% yolk. Minor variations do occur due to factorssuch as breed, age of bird, nutrition and disease.

Table 1 gives the approximate physical composition of a newly-laid egg.

The proportion of the thick to thin albumen varies greatly, evenin newly laid eggs due to factors such as bird age and health. Some-times, even newly laid eggs contain little or no thick albumen.

Table 1 Percentage physical composition of the egg

Nutrient ContentThe typical gross chemical composition of the edible part of anegg is summarised in Table 2. It is possible to change thequantity of certain nutrients in eggs by changing the diet of thelaying hen. For example, the amount of polyunsaturated fattyacids can be increased at the expense of saturated fat. Similarlyit is also possible to enrich eggs with additional vitamins andminerals if required.

Shell 11%True Shell 97

Membranes 3

100

Albumen 58%Chalazae 3

Inner Thin 17

Outer Thick 57

Outer Thin 23

100

Yolk 31%

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4 Compos it ion & nutr ientcontent o f eggs

15

Table 2 Composition of eggs per 100 grams (excluding shell)

Sect ion One

Whole Egg Albumen YolkWater (g) 75.1 88.3 51.0

Protein (g) 12.5 9.0 16.1

Fat (g) 10.8 Trace 30.5

Carbohydrate (g) Trace Trace Trace

Energy Value (kJ) 612 153 1402

Immediately after the egg is laid, the internal contents and structurebegin to change. This is a continual, irreversible process andeven the most carefully controlled storage conditions can do nomore than slow down the rate of deterioration. The main changeswhich occur are outlined below.

The Air SpaceWhen the egg is laid, it is warmer than its surroundings. As itcools, the contents contract and a small air space is formedbetween the inner and the outer shell membrane. The air spacenormally (but not always) forms at the broad end of the eggbecause there are more pores in this part of the shell.

As the egg ages, moisture and carbon dioxide continue to belost through the pores. Air moves in and the air space increasesin size at a rate which is determined by the temperature and therelative humidity of the surrounding air. The warmer and drierthe air, the quicker the moisture loss from the egg. The size(height) of the air space is used as an approximate guide to thequality and age of an egg.

Albumen QualityIn a very fresh, good quality egg, the albumen is jelly-like and mayhave a cloudy appearance. As the egg ages and carbon dioxideis lost through the shell, the contents become more alkaline andthis causes the albumen to become transparent and increasinglywatery. At higher temperatures, the rate of carbon dioxide loss ishigher and the visible signs of ageing occur quicker.

The quality of albumen can be assessed by measuring the height inmillimetres of the outer thick albumen. The height of the albumenand the weight of the intact egg is used to calculate the HaughUnit value.

It is the proteins in the thick albumen which begin to breakdown during storage as the egg becomes more alkaline. At thesame time, water slowly migrates into the yolk and the shell fromthe albumen so that both may develop a mottled appearanceand the yolk becomes enlarged and flattened on breakout. Theyolk moves away from the centre of the egg and may eventually

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5 E ffects of storage upone g g q u a l i t y

Mottled yolks

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rest against the shell itself. This breakdown of the albumenmakes the egg extremely vulnerable to microbial invasion.

Eggs are food. Like all foods, they must be assessed for quality toensure that they are acceptable to the customer. Failure toremove defective eggs can lead to complaint, loss of businessand prosecution.

Every day, over 26 million eggs are produced in the UK.Successful quality control requires a combination of skill,concentration and practice. Gradually, automatic andmechanical developments have emerged which have reducedreliance on the human eye. However, much of this technology iscurrently affordable only to larger businesses and even whenused, there is a need for supporting visual quality checks.

2 Quality standards – The EUmarketing regulat ions andother cont ro ls

A formal inspection must be undertaken so that each egg can beallocated to a particular Quality Class. These Classes are definedin the EU Egg Marketing Regulations which are enforcedthroughout all European Union (EU) countries. There are threequality classes for eggs intended for human consumption. Inbrief, these are:

• Class A (‘fresh eggs’). These may further be sold as‘Extra’ Fresh if the air space is less than 4mm in height atthe time of candling and throughout its marketable sevendays from packing.

• Class B (‘certain second quality or preserved eggs’).

• Class C (‘non graded eggs intended for the manufactureof foodstuffs for human consumption’).

Table 3 (see p18) provides further details of the minimumpermissible standards for each Class.

Sect ion Tw o

1 Grading of eggs for human consumption

Class A egg –external

Class A egg –internal

In practice, Class B eggs are seldom marketed and the mainclasses are A and C. All eggs sold in UK supermarkets andsimilar retail shops will be Class A. Class C eggs are normallysent to processing plants for pasteurisation. Any egg which failsto meet the Class C criteria is unfit for human consumption andis classed as an ‘Industrial Egg’. Typically, eggs with brokenshells (i.e. where the shell membranes have been broken) fallinto this category. Industrial eggs can be used for non-food usesif suitable markets can be found.

Table 3 Minimum quality standards for eggs of Classes A, B and C

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Class A egg

Class A egg (extrafresh)

Class A

Cuticle Normal, clean, undamaged

Shell Normal, clean, undamaged

Air Space Height not exceeding 6mm(4mm for Extra Fresh) Stationary

Albumen Clear, limpid, of a gelatine-like consistency, free of allforeign bodies of any kind

Yolk Visible on candling as ashadow only, without clearlydiscernible outline, notmoving appreciably awayfrom the centre of the eggon rotation, free from allforeign bodies of any kind

Germ Cell Imperceptible development

Smell Free of foreign smell

Wet or dry cleaning Not permitted

NOTES (for guidance only)

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In some cases, certain customers may impose their own buyingrequirements which exceed the minimum Class A standards.These may relate to the colour of the shell, the condition of thealbumen (e.g. a minimum Haugh Unit score) or any other aspectof quality. Where this is the case, it is up to packing centres toincorporate these requirements into their normal inspectionprocedures.

Sect ion Tw o

Class B Class C

Dirty, damaged, treated Dirty, damaged, treated

Normal, undamaged Cracked, misshaped, rough texturedor any other abnormality

Height not exceeding Height exceeding 9mm or damaged 9mmMobile

Clear, limpid, free of all Clear, no discolouration or turbidity,foreign bodies of any small foreign bodies permissiblekind

Visible on candling as a Distinct on candling, ‘sided’ or,shadow only, free from ‘stuck’, no discolouration, smallall foreign bodies of foreign bodies permissibleany kind

Imperceptible Imperceptibledevelopment development

Free of foreign smell Free of foreign smell

Permitted Permitted

This category includes This category includes variousnaturally dirty shelled shell faults and dry cracked eggsand washed eggs (membranes unbroken)

Class A

Cuticle Normal, clean, undamaged

Shell Normal, clean, undamaged

Air Space Height not exceeding 6mm(4mm for Extra Fresh) Stationary

Albumen Clear, limpid, of a gelatine-likeconsistency, free of all foreign bodiesof any kind

Yolk Visible on candling as a shadow only,without clearly discernible outline,not moving appreciably away from the centre of the egg on rotation, free fromall foreign bodies of any kind

Germ Cell Imperceptible development

Smell Free of foreign smell

Wet or dry cleaning Not permitted

NOTES(for guidance only)

Class B Class C

Dirty, damaged, treated Dirty, damaged, treated

Normal, undamaged Cracked, misshaped, rough texturedor any other abnormality

Height not exceeding Height exceeding 9mm or damaged 9mmMobile

Clear, limpid, free of all Clear, no discolouration or turbidity,foreign bodies of any small foreign bodies permissiblekind

Visible on candling as a Distinct on candling, ‘sided’ or,shadow only, free from ‘stuck’, no discolouration, smallall foreign bodies of foreign bodies permissibleany kind

Imperceptible Imperceptibledevelopment development

Free of foreign smell Free of foreign smell

Permitted Permitted

This category includes This category includes variousnaturally dirty shelled shell faults and dry cracked eggsand washed eggs (membranes unbroken)

Table 3 Minimum quality standards for eggs of Classes A, B and C

A number of common quality faults can be seen by closeinspection of eggs under normal lighting conditions. However,candling can reveal many other defects which may otherwisenot be visible.

For 70 years, egg candling has played a fundamental role in themarketing of eating eggs in the UK. The technique takes itsname from the original source of light used – the candle. Abeam of light is shone through the shell so that the contentsbecome visible.

The limitations of candling have long been recognised, but formany years, it provided the best way of identifyinghairline cracks in shells and the only way ofidentifying internal faults without breaking the shell.Recently, automatic in-line detection equipment forcracked eggs and other faults has been developed andis now in use in larger packing centres to assist qualitycontrol staff.

Inspection of eggs in commercial packing centrescan be divided into individual egg and mass eggsystems. The objectives and methods used aresummarised below.

Individual Egg Quality Control SystemsIn many packing centres, eggs are graded from a large numberof different flocks and it is important to get an overall assessmentof the quality of each consignment before grading. The resultsobtained from testing a small sample of eggs can be used todetermine the order of grading, the customer, the grading speedand the number of inspection staff needed.

Assessments can be made by Individual (or Hand) Candling orby Break Out and related Laboratory Tests. In many cases, bothtests will be undertaken.

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Automatic crackdetection unit

(Picture reproduced by kind

permission of Moba)

3 Qual i ty contro l methodsf o r eggs

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Individual (Hand) CandlingIn very small enterprises, hand candling may be the most costeffective way of assessing the quality of all eggs. In largerbusinesses, it is used to identify levels and types of faults inrepresentative samples of ungraded and graded eggs. It is acondition of the EU Egg Marketing Regulations that gradingequipment should include an independent candling lamp.

Candling Lamp DesignA typical design of candling lamp is shown here. The key designfeatures are that:

• the light should be focused onto the aperture.

• cushioning material should be fitted around the apertureto minimise leakage of light when the egg is in place.

• the aperture should not exceed 30mm in diameter.

Hand Candling Techniques• Direct the aperture away from the eye of the candler to

avoid glare.

• Keep the background in the candling area as dark aspossible.

• Hold the broad end of the egg to the aperture and thenturn the egg so that all the surface area has been seen.

• The visibility and movement of the yolk and any internalfaults should be observed as the egg is turned.

• A standard record sheet should be used to enter thenumber and type of faults.

For maximum speed of candling, the operator should aim tohold two eggs in each hand at a time. MAFF Egg MarketingInspectors and ADAS offer training courses on the techniquesused.

Break-Out/Laboratory TestsIn order to provide more detailed information on aspects ofquality and consumer preference, break-out and other laboratorytests are undertaken on representative samples of eggs.

Sect ion Tw o

Hand candling of eggs

Typical consumer preferences include freshness, shell andalbumen quality and shell and yolk colour. At best, candlingand other visual assessments can provide a guide but moredetailed measurements are needed to ensure that customerneeds are met.

Detailed break-out tests take time to complete and because thetested eggs are unsaleable, only small numbers can be used.Eggs from a single flock of a given age are reasonably consistentand so a fairly small sample can provide a useful indication tothe average quality of eggs from the whole flock.

Equipment for measuring the shell and yolk colour and shell andalbumen quality is now commercially available and used widelywithin UK packing centres. All measurements can beautomatically recorded and compared with standard and targetfigures.

Mass Egg InspectionAs the scale of individual businesseshas increased and technology hasadvanced, so the methods usedhave changed.

Traditional commercial machinesmay grade around 100 cases of eggs(3,000 dozen) per hour. In thelargest packing centres, up to 300cases of eggs may be graded per

hour on a single machine. The higher throughput machinesgenerally incorporate more automation so that identification offaults and segregation of second quality eggs is easier.

At the packing centre, mass egg inspection normally takes placein two stages. First of all, an initial pre-candling or pre-selectiontakes place, followed by the main candling process.

Pre-Candling ProceduresThe aim of pre-candling is to remove eggs with visible faults. Inparticular, it should succeed in removing gross faults such aseggs with dirty, glazed (wet), weak, coated, badly cracked or

22

Modern equipment formeasuring egg quality

(Picture reproduced by kind

permission of TSS Technical

Services and Supplies (York))

23

misshaped shells. A particular priority is to remove eggs withfaults which may contaminate other eggs.

The main requirements for successful pre-candling are asfollows:

• It should take place shortly after the eggs have beenloaded.

• Eggs should be viewed under normal but high intensitylight.

• It should be possible for the pre-candler to see themajority if not all of the surface of the egg.

• The number of pre-selection staff needed and thethroughput speed should be determined by the expectedquality of the incoming eggs.

• A comfortable working environment and regular breaksare needed if high standards are to be maintained.

• Pre-candling staff should be suitably trained and theirperformance regularly assessed.

Mass Egg CandlingEgg candling is an immensely difficult task which requires skill,practice and concentration. Eggs pass through the booth inparallel rows on rollers. A single candler working on a 100 casesper hour grading machine has to inspect 10 eggs per second andremove perhaps one of them.

Candling should be seen as one part of a larger inspectionprocess at the packing centre. The starting point is pre-candling.If effective, this allows more attention to be placed on faultswhich cannot be seen under normal light, such as ‘hairlinecracks’ and internal faults.

Candling Facilities• Successful candling requires an enclosed booth, free

from external light.

• Eggs should be illuminated from beneath using highintensity lighting.

Sect ion Tw o

Commercial scale eggcandling

(Picture reproduced by kind

permission of Moba)

• A mirror should be incorporated and so positioned as toenable the candler to see both ‘poles’ of each egg.

• Both the mirrors and the covers over the lights must bekept clean and dust-free to ensure good visibility.

• The candler should be able to work (whether standing orsitting) in surroundings which are comfortable and theheight of the platform or seat should be adjustableaccording to the height of the candler.

Candling Personnel• Candlers should have good eyesight and should be

encouraged to have regular eye examinations.

• Regular breaks from candling are essential and no oneshould be required to spend more than 30 minutes in thebooth at any one time.

• Candlers should not be expected to perform any othertasks whilst in the booth.

Candling Procedures• To reduce glare from the lights, a throughput of eggs

should be maintained which ensures that the rollers areas full as possible.

• The throughput speed of the grader must be geared to thequality of eggs being assessed and the parameter speedsfor correct ink-jetting onto egg shells where fitted.

• If the rollers become wet due to broken eggs, the gradershould be stopped so that cleaning can take place.

• The candler should concentrate on the eggs within aparticular small zone within the booth and eggs withinthat zone should be examined in a logical sequence,with the mirrors being used as necessary.

• If in doubt, an individual egg should be removed fromthe rollers and examined more closely at a convenientmoment.

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• In addition to shell faults, the experienced candler shouldbe able to assess:

– the size and position of the air space

– the appearance and movement of the yolk (whichprovides an indication of albumen quality)

– whether the egg contains inclusions such as blood ormeat spots.

• In conventional systems, eggs with faults must beremoved by hand and put onto conveniently placedkeyes trays or into buckets.

• In semi-automated, higher throughput systems, eggsidentified as seconds may be electronically marked bythe candler so that they are automatically diverted to theseconds lane.

• In systems which include automatic detection of cracksand certain other faults, the candler is free to concentrateon other aspects of quality which require visualidentification.

Sect ion Tw o

Air SpaceThe space which forms between the inner and outer shellmembranes as a result of air movement through the egg shellpores. The size of the air space increases during storage.

AlbumenAlso known as ‘egg white’ it is rich in protein and vitamins andprovides support and protection for the yolk.

CandlingA quality control procedure which allows assessment of internalegg quality and easier identification of certain other faults,particularly hairline shell cracks.

ChalazaeTwisted, fibrous structures which extend outwards through thealbumen and hold the yolk in place in the centre of the egg.

ClutchA sequence of daily egg laying by an individual bird which isseparated from other sequences by one or more ‘pause days’ onwhich no eggs are laid.

CuticleThe outer coating of the egg shell which gives the egg itscharacteristic bloom or shine.

Germ Cell (Germinal Disc)Sometimes identified on the surface of the yolk as a disc ofslightly different colour, the germ cell is the site of cell division ifthe egg has been fertilised.

GradingThe classification of eggs by Quality (Classes A, B, C andIndustrial) and into weight bands as defined by EU EggMarketing Regulations.

Haugh UnitA measurement made to determine albumen quality. The HaughUnit is calculated from the height of the thick albumen and theweight of the intact egg.

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Glossary of terms

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OvaryThe reproductive organ of the laying hen in which the egg yolksdevelop.

OviductA long tube-like organ in the laying hen which accepts the yolkafter ovulation and is responsible for the remainder of the eggformation process.

OvipositionThe name for the process of laying an egg.

OvulationThe release of the yolk from the ovary into the oviduct.

Ovum (plural: ova)Commonly known as the yolk, the ovum consists of the vitallinemembrane, the germ cell and the yolk material.

PoresTiny holes in the egg shell which permit movement of air andmoisture between the egg and its surroundings.

ShellThe outer covering of the egg which is largely composed ofcalcium carbonate.

Shell GlandThe part of the oviduct which is responsible for shell formation.

Shell MembranesThe innermost part of the egg shell (visible in so-called ‘shell-less eggs’) which acts as the foundation upon which the trueshell is built.

Vitalline MembraneA see-through barrier which surrounds and contains the yolk.

YolkConsists of fats, vitamins and minerals and about half of theegg’s total protein content.

Sect ion Three

Pictoria l gu ide to egg qual i ty

Freshness and albumen quality

1 Class A Egg

5 Egg with good quality, gelatinous albumen

Class A Egg showing air space < 6mm 2

Egg with watery albumen 6

3 Extra Fresh Class A showing air space < 4mm Class B Egg showing air space > 6mm 4

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Shell faults

7 Shell-less Egg

11 Equatorial Bulge

Soft-shelled Egg 8

Crinkled Shell 12

9 Target or Thumb-print Type Slab-sided Egg 10

Sect ion Four

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13 Rough Shell Pale Shell 14

15 Calcium Splashed Lilac/Pink Shell 16

Shell faults (cont’d)

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19 Pinhole Crack (Candled) Hairline Crack 20

Sect ion Four

17 Star Crack Star Crack 18

Cracked eggs

Dirty eggs

21 Faeces

25 Glazed or Varnished with Yolk

Urate 22

Glazed or Varnished with Albumen 26

23 Oil/Tar Blood 24

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27 Typical Range of Yolk Colours

31 Meat Spot

Double Yolked Egg 28

Meat Spot in Intact Egg 32

29 Mottled Yolk Internal Mould (Microbial Invasion) 30

Sect ion Four

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Internal quality

Internal quality (cont’d)

33 Blood spot Mobile airspace 32

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