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Operational procedure: Shell egg grade verification

Requirements for the Safe Food for Canadians Regulations

Although the Safe Food for Canadians Regulations (SFCR) came into force on January 15, 2019, certain requirements may apply in 2020 and 2021 based on food commodity, type of activity and business size. For more information, refer to the SFCR timelines.

On this page

1.0 Purpose

The purpose of this document is to provide Canadian Food Inspection Agency (CFIA) inspection staff on standard commodity inspection procedures related to grade verification of shell eggs. These inspections will verify that shell eggs are safe, wholesome and meet the requirements of the Safe Food for Canadians Act and Regulations and the Food and Drugs Act and Regulations.

The guidance outlined below may be used when verifying compliance of imported shell eggs, to support export certification of shell eggs, to aid in assessment of a Preventive Control (PC) related sub-element, as part of a food safety investigation, or as follow-up to a complaint.

This document is intended to be used in conjunction with other guidance documents as referenced in Section 3.0.

2.0 Authorities

The inspection powers, control actions and enforcement actions authorized by the above legislation are identified and explained in the Operational guideline: Food regulatory response guidelines

3.0 Reference documents

4.0 Definitions

Unless specified below, definitions are located in either the:

The following definition is taken from the above mentioned references and is essential for the application of this guidance:

egg
means an egg of a domestic chicken of the species Gallus domesticus

5.0 Acronyms

Acronyms are spelled out the first time they are used in this document and are consolidated in the Food business line acronyms list.

6.0 Operational procedure

This operational procedure provides inspection guidance specific to shell egg grade verification. Shell eggs are sampled and inspected to ensure that regulatory requirements for grade (which includes criteria for safety and quality) are met.

Grading eggs normally includes cleaning (usually by washing), candling, weighing (Canada A and B) and packing into containers with the applicable federal grade name.

There are four grades of eggs under the Canadian grade compendium: Volume 5 - Eggs. These are Canada A, Canada B, Canada C and Canada Nest Run (CNR). Grading and application of grade names under the SFCR is limited to inspectors and to licenced egg operators.

Eggs in a container marked with a federal grade name must meet the requirements of the grade indicated until the end of the best before date. The best before date is the date before which there has been no appreciable deterioration in the quality of the product since it was packaged and displayed for sale, providing that it is kept under satisfactory conditions.

Where more specific guidance is required then what is provided in the SIP, these will be indicated in this section.

Commodity inspection OGs refer the inspector to the SIP for basic guidance on the four (4) inspection steps. If the commodity inspection is being conducted to support a preventive control inspection (PCI) currently underway, some or parts of the inspection steps will have already been completed.

6.1 Prepare for inspection

Refer to SIP, section 3, step 1. In addition to the general guidance provided in SIP, the following applies.

Table 1. Recording inspection data in Digital Service Delivery Platform (DSDP)
Trigger

Pick one of the following triggers, as appropriate:

  • Preventive Control Inspection Plan
  • Commodity Inspection Plan
  • Incident Response
  • Export Permission
  • Import Permission
Inspection task type Commodity Inspection
Inspection level 1 task Perform test
Inspection level 2 task Grade verification

6.1.1 Prepare the toolkit

In addition to the list of equipment found in section 3.5 of the SIP, the following equipment is needed to complete the grade verification:

6.2 Conduct the inspection

Refer to SIP, section 4, step 2 and to SIP, section 4.4.3. In addition to the general guidance provided in the SIP, the following applies.

6.2.1 Locate and identify the lots

A lot is a quantity of eggs that for any reason is considered separately from any other quantity of eggs for the purpose of an inspection.

A lot should only contain one size of eggs. As an example, the inspector could designate a lot of eggs using brand, unique expiry date or packed on date, or a specific number of pallets of eggs, all within one size.

Determination of the number of units in the lot (N)

A unit is any container of 60 to 180 eggs (5 to 15 dozen). Only 60 eggs are selected from within the unit. If the eggs are packed in containers of more than 15 dozen, the inspector should determine the definition of a unit prior to selecting the sample. To maintain the statistical validity of the sampling plan, a unit must not contain more than 180 eggs (15 dozen). For example, the inspector may decide that each 24 dozen case will be 2 × 12 dozen units and assign a number to each 12 dozen unit.

Determination of the sample size (n)

The sampling procedure consists of drawing from the lot, at random, the designated number of units (n) of product required to make up the sample as determined by the appropriate sampling plan found in Appendix 1.

Selection of units using the random sampling numbers table

Use the Random Sampling Numbers Table found in the Operational guideline: General principles of sampling – food products, environments, water and ice to select the units for inspection.

6.2.2 Grade assessment criteria

The criteria for grading shell eggs are found in the Canadian grade compendium: Volume 5 – Eggs.

Rejects

Eggs that have undergone grading assessment and do not meet the requirements in respect of any grade are considered rejects [SFCR 333(1)]. Rejected eggs must be destroyed or be placed in a container that is labelled with the words "Reject" and "Rejetés" [SFCR 333(2)].

Any egg having any of the following characteristics is considered a reject:

6.2.3 Types of grade verifications

6.2.3.1 Grade verification at origin

A grade verification at origin is done when the product inspection:

Product assessment

The units should be candled and assessed against the grade requirements. The Shell egg - Product inspection report - Origin (CFIA/ACIA 4196 - internal access only) may be used to record inspection observations.

Eggs that do not meet the requirements for the grade at which they were graded are considered under-grade [Canadian grade compendium: Volume 5 – Eggs].

During assessment, an egg is only counted under 1 category with the most serious defect taking precedence (reject, leaker, then under-grade). For purposes of determining acceptability of the units, eggs that have cracked shells, and are under-grade for a reason other than cracks must be counted as a crack. Counting one egg in two categories is not acceptable.

The under-grades for each unit should be recorded separately.

Eggs that are under-grades, leakers or rejects should be segregated for proper disposition.

Acceptable unit:

A unit in a lot is acceptable if, from the 60 eggs drawn and examined, a maximum total of 4 under-grades including cracks are found, of which not more than 3 are under-grades for reasons other than cracks. Leakers and rejects are not considered in the evaluation of an individual unit.

Defective unit:

A unit is defective if a total of at least 5 under-grades including cracks are found or at least 4 under-grades are found for reasons other than cracks.

The acceptability of the lot is based on two evaluations;

In order to determine the acceptability of a lot, an Acceptance Number (Ac) and Rejection Number (Re) are required. These numbers are determined by using the sampling plans in Appendix 1 Table 1 and Table 2.

Ac = the maximum number of defective units allowed in the sample for a lot to be accepted.

Re = the minimum number of defective units in the sample requiring the lot to be rejected.

Acceptable lot: A lot is acceptable if the number of defective units found in the sample is equal to or less than the Ac for the appropriate sample size.

Reject lot: If the number of defective units is equal to or greater than the Re, the lot fails and will be detained.

Administrative tolerances for Grade A, B and C product verified at origin

In addition to the evaluation of the lot based on the Ac and Re numbers, the administrative tolerance for product inspected at origin is also applied. The administrative tolerance allows for some leakers and rejects in the lot.

Administrative Tolerances at Origin
Leakers Stain > 1/3 Table Note 1 Reject Table Note 2
Canada A /B 1 per 2 units Table Note 3 1 per unit
Canada C 1 per unit 3 per unit 1 per unit

Table Notes

Table Note 1

Regulated tolerance – Canadian grade compendium: Volume 5 – Eggs, section 7 (2).

Return to table note 1  referrer

Table Note 2

Dirts included in the Reject administrative tolerance for Canada A, Canada B and Canada C

Return to table note 2  referrer

Table Note 3

A unit consists of 60 eggs (5 dozen eggs)

Return to table note 3  referrer

The number of leakers and rejects in the lot should be calculated as an average for the lot at the end of the inspection and compared to the administrative tolerance. If the number of reject eggs or leakers found during the inspection is more that the Administrative Tolerance, the lot fails and will be detained, even if the Ac of units was met.

Example: A lot of 200 boxes of Canada C eggs are inspected. The sample size is 5 units (Table 1 is used to determine sample size for Canada C). 60 eggs from each of the 5 units are inspected. The following results were found

Results of example sample:
Unit 1 2 3 4 5 Total
Leakers 1 2 0 2 0 5
Rejects 0 3 1 1 2 7

All under-grades from each sample are to be removed and identified to the establishment so that they are not dispersed back into the sample.

6.2.3.2 Grade verification at destination

A grade verification at destination is any inspection carried out at a place other than where the eggs were graded or packed (for example, at a wholesaler, retailer, distributor, breaking establishment, and grading establishment).

Grade verification at destination sampling plan

A grade verification at destination uses the sampling plan which can be found in Appendix 1, Table 3. The sampling plan applies to Grade A and B eggs. For Canada C eggs at destination, Appendix 1, Table 3 is used to determine sample size only, since the tolerance for cracks and under-grades do not apply. Canada C eggs are inspected for leakers and rejects only.

Product assessment

The units should be candled and assessed against the destination tolerance. The Shell egg destination report (CFIA/ACIA 1017 - internal access only) may be used to record inspection observations.

Set aside the under-grades found in the units inspected. Under-grades should be separated into cracks, and under-grades other than cracks. Eggs that have cracked shells, and are under-grade for a reason other than cracks must be counted as a crack. Counting one egg in both categories is not acceptable. Rejects and leakers will be considered separately. During assessment, an egg is only counted under 1 category with the most serious defect taking precedence (reject, leaker, then under-grade).

Count the total number of cracks in the sample inspected. Subtract the crack tolerance (3%) from the total number of cracks. Add the number of remaining cracks to the number of under-grades other than cracks. This total number must not exceed 7%.

Example: A lot contains 80 boxes of eggs. Appendix 1, Table 3 indicates that 4 units are to be selected for sampling and 240 eggs are to be examined. Upon examination, the sample of 240 eggs was found to have 12 cracks and 14 under-grades other than cracks. Appendix 1, Table 3 shows that the crack tolerance (3%) is 7.2 eggs.

Evaluation of the lot based on the destination tolerance
Instructions Calculations
1. Subtract the crack tolerance (Table 3: 3% cracks) from the total number of cracks in the sample 12 cracks in sample - 7.2 crack tolerance = 4.8 remaining cracks
2. Add the number of remaining cracks to the number of under-grades other than cracks 4.8 remaining cracks + 14 under-grades other than cracks = 18.8 total under-grades
3. Compare total under-grades in lot to the value in Table 3 (7% tolerance) 18.8 total under-grades is greater than (>) the 16.8 under-grades allowed

Since the number of total under-grades exceeded the 7% tolerance, the lot fails.

Administrative Tolerances for Canada A, B and C Inspected at Destination

In addition to the evaluation of the lot based on the destination tolerance, the administrative tolerance for product inspected at destination is also applied. The administrative tolerance allows for some leakers and rejects in the lot.

Administrative Tolerances at Destination
Leakers Stain > 1/3 Table Note 4 Reject Table Note 5
Canada A /B 1 per unit Table Note 6 1 per unit
Canada C 3 per unit 3 per unit 1 per unit

Table Notes

Table Note 4

Regulated tolerance – Canadian grade compendium: Volume 5 – Eggs, Section 7 (2)

Return to table note 4  referrer

Table Note 5

Dirts are included in the administrative reject tolerance

Return to table note 5  referrer

Table Note 6

A unit consists of 60 eggs (5 dozen eggs)

Return to table note 6  referrer

The number of leakers and rejects in the lot should be calculated as an average for the lot at the end of the inspection and compared to the administrative tolerance. If the number of reject eggs or leakers found during the inspection is more than the Administrative Tolerance, the lot fails and will be detained, even if the number of under-grades was found to be acceptable.

Any under-grade eggs that are found to be within the tolerance for the number of samples examined may be dispersed throughout the samples. Any rejects or leakers that were found during the inspection are to be discarded.

6.2.3.3 Grade verification of Canada Nest run
Product assessment

The units should be candled and the acceptability of the lot assessed. The Pre-grade/Canada nest run product inspection report (internal access only - CFIA/ACIA 5427) may be used to record inspection observations.

At origin, Canada Nest Run eggs must meet the requirements set out in the Canadian grade compendium: Volume 5 - Eggs.

At destination, a tolerance is applied to allow for damage that may occur during transportation. The origin requirements and destination tolerance for Canada Nest Run eggs can be seen in the table below.

Origin requirements and destination tolerance for Canada Nest Run eggs
Defect Origin Destination
Cracked shells 10% 13%
Dirt >160 mm2 5% 5%
Leakers or Rejects 3% 5%
Total Maximum 15% 20%
Completing the inspection

Any eggs that are found to be within the tolerance may be dispersed throughout the samples. Any rejects or leakers that were found during the inspection are to be discarded since leakers and rejects are not eligible for breaking or grading.

6.2.3.4 Pre-grade commodity inspection

Prior to grading eggs as Canada A, the incoming eggs must meet the requirements set out in the Canadian grade compendium: Volume 5 - Eggs subsection 4(2). The operator is responsible to ensure that incoming eggs meet these requirements for the production and marketing of high quality shell eggs. The pre-grade assessments done by the operator also contribute to food safety by reducing the number of excessively dirty, cracked, or weak shelled eggs that go through the washing process. These eggs may increase the egg solids and fecal content of the wash water, contributing to unacceptable conditions.

A pre-grade commodity inspection may be conducted by CFIA inspection staff to help support a preventive control inspection (PCI) to verify that the operator’s PC meets the regulatory requirements. The pre-grade inspection procedures are outlined below. A lot of ungraded eggs that fails to meet the pre-grade requirements upon inspection, is not eligible to be graded as Canada A. The Pre-grade/Canada nest run product inspection report (CFIA/ACIA 5427 - internal access only) may be used to record inspection observations.

In some provinces, provincial pre-grade programs exist. In such provinces, the inspector should keep on file a copy of the provincial pre-grade program from each province where ungraded eggs are received. The provincial pre-grade program will identify who and how to distribute failed pre-grade commodity inspections.

Selection of producer

The Provincial Egg Marketing Board may provide the CFIA, upon request, a list of all registered quota holding egg producers in the province. These lists will be available at the request of the inspection supervisor for distribution to the inspectors. The list from the provincial board should include the flock age, flock size and the name of the egg establishment to which the eggs are shipped. Alternatively, the CFIA may request that an egg establishment provide a list of egg producers who ship to their facility. The list from the egg establishment should include flock age, flock size and day of the week on which the producer typically ships.

For inspection purposes, the CFIA inspector may target flocks based on the following:

CFIA inspectors may inspect eggs from a particular flock upon request on a cost-recoverable basis.

Inspection procedure

Sample size is determined using the Nest Run/Pre-grade sampling plan in Appendix 1, Table 4. The eggs are candled and assessed against the pre-grade requirements listed below.

Haugh units are considered in the assessment of the lot. Twenty (20) eggs, chosen at random from the total sample drawn are broken out to determine the quality of the albumen using a Haugh unit micrometer. See Appendix 3 for instructions on Haugh Unit determination.

Product assessment

The sample of eggs is assessed based on the Pre-grade requirements below. A summary of pre-grade requirements can be found in table format in Appendix 2.

Pre-grade lot of eggs will fail if:

Failed inspections:

Provinces with a Pre-grade inspection program:

Provinces without a Pre-grade Inspection Program

Non-Quota Holders

6.2.3.5 Verification of shell eggs intended for further processing

All grades of shell eggs (Canada A, B, C, Canada Nest Run) as well as ungraded eggs may be used to produce processed egg products provided processes are in place to bring Canada Nest Run and ungraded eggs to the requirements found in SFCR 102. Further information on how industry can meet this requirement is provided in Regulatory requirements: Processed egg products.

Section 6.2.3.2 Grade verification at destination is used to conduct shell egg grade verifications for eggs intended for further processing.

6.2.4 Determine compliance

The assessment criteria for each type of grading inspection are found in sections 6.2.2 Grade assessment criteria and 6.2.3 Types of grading inspection. If a non-compliance is identified, refer to SIP, section 4.5, and to SIP, section 4.6.

6.2.5 Capturing notes related to commodity inspection in DSDP

For information on capturing notes relating to commodity inspections in the DSDP, refer to Appendix A section 5.4.1 of the SIP and section 3.5.1 of the DSDP SOP INS - conducting an inspection (internal access only - RDIMS 9839405).

In addition to capturing an accurate description (brand name, common name, net quantity, lot number) of the commodity inspected in the "Commodity Description" field in DSDP, enter the same commodity description in the "objective evidence" field along with the non-compliances found so that it appears in the final inspection report.

Worksheets used as tools to aid in the compliance decision of the grade verification should be saved as an RDIMS file and referenced in the "Notes" section of the document record of the inspection task record in DSDP. Upon request, the worksheet may be given to the licence holder.

6.3 Communicate the results

Refer to SIP, section 5, step 3.

6.4 Conduct follow-up

Refer to SIP, section 6, step 4.

For general inquiries related to this operational guidance document, please follow established communication channels, including submitting an electronic Request for Action Form (e-RAF)

7.0 Appendices

Appendix 1: Sampling plans

Appendix 2: Pre-grade and grade requirements table

Appendix 3: Haugh Unit Determination

Appendix 1: Sampling plans

An origin inspection uses one of the two sampling plans shown below in Table 1 and Table 2. The sampling plans are based on size designation and grade:

Note

These sampling schemes were developed based on the International Standard ISO/2859/1, using Acceptable Quality Levels (AQL). The AQL is a designated value of percent defectives (nonconforming) or defects (nonconformities) per hundred units that will be accepted most of the time by the acceptance sampling procedure to be used. An AQL of 25.0% was selected for Canada A Jumbo Size and Extra Large Size and an AQL of 10.0% was chosen for all other grades and sizes.

Both the lot size (N) and the inspection level are required to determine the number of units to be selected for the sample (sample size n). There is currently only one level of inspection: the former Normal level.

Example: If a lot contains 600 boxes of ALS eggs, Table 1 is used to determine the sample size. At the inspection level for that grade/size of egg, the sample size is 32 units.

Note

In some sections of the sampling plans, where the lot size is at the low end of the 2 to 90 or 2 to 15 unit range, the sample size may exceed the lot size (Table 1). In such cases, the following steps should be taken:

  • the inspector should first determine if the size of the units in the lot can be re-evaluated. For example, if the units were numbered as boxes of 15 dozen, unit numbers could be reassigned by splitting the boxes into 3 units of 5 dozen to increase the total number of units in the lot. Inspectors must keep in mind that a unit must contain a minimum of 60 eggs (5 dozen). If, by splitting the units, the required sample size can be met, proceed with the inspection as usual
  • if the units cannot be reduced in size, the number of units in the lot will remain smaller than the sample size. In these cases, 100% of the eggs must be examined. When evaluating the acceptability of the lot, the Ac and Re numbers would not apply. The acceptability of the lot should be determined using the following percentages: no more than 7% total under-grades and no more than 5% under-grades excluding cracks
Table 1: Origin sampling plan for Canada A sizes (except Jumbo Size and Extra Large Size) and Canada B
Lot size (number of units) Inspection level
sample size
Inspection level
Ac
Inspection level
Re
2 - 90 5 1 2
91 - 150 8 2 3
151 - 280 13 3 4
281 - 500 20 5 6
501 - 1200 32 7 8
1201 - 3200 50 10 11
3201 - 10,000 80 14 15
over/plus 10,000 125 21 22

Ac = Acceptance number
Re = Rejection number

Table 2: Origin sampling plan for Canada A Jumbo Size and Extra Large Size
Lot size (number of units) Inspection level
sample size
Inspection level
accept
Inspection level
reject
2-15 2 1 2
16-25 3 2 3
26-90 5 3 4
91-150 8 5 6
151-280 13 7 8
281-500 20 10 11
501-1200 32 14 15
over/plus 1200 50 21 22

Inspection of Canada C: For inspection of Canada C eggs at origin, Table 1 is used to determine the sample size, but Ac and Re numbers do not apply. Canada C eggs are inspected for leakers and rejects only, and are assessed based on the administrative tolerance described above.

Examples - Origin inspection

Example 1: Consider a lot of 280 boxes (units) of 15 dozen Canada ALS eggs, being inspected at origin. Table 1 requires that a sample of 13 boxes be randomly selected for inspection and that 60 eggs be examined from each box to determine its individual acceptability. Upon inspection, the following results are obtained:

Results from origin inspection example 1
Unit in sample Undergrades, excluding cracks Total undergrades, including cracks Classification of unit
1 0 2 acceptable
2 3 3 acceptable
3 2 4 acceptable
4 2 2 acceptable
5 1 4 acceptable
6 0 2 acceptable
7 0 3 acceptable
8 4 4 defective
9 1 2 acceptable
10 0 2 acceptable
11 6 7 defective
12 2 4 acceptable
13 3 4 acceptable

Applying the definition of a defective unit, two boxes have been found defective, namely box 8 and box 11. According to the sampling plan, the Ac is 3, permitting as many as 4 units (boxes) to be defective in an acceptable lot. Consequently, the above lot of eggs is deemed acceptable and passes. The administrative tolerance for leakers and rejects would still have to be considered before the final assessment of the product was made.

Example 2: A lot of 80 boxes (units) of 15 dozen Canada AELS eggs is to be inspected at origin. Using Table 2 a random sample of 5 units needs to be drawn and 60 eggs per box examined for possible under-grades. Assume the following results are recorded:

Results from origin inspection example 2
Unit in sample Under-grades, excluding cracks Total under-grades, including cracks Classification of unit
1 2 5 defective
2 3 3 acceptable
3 2 6 defective
4 1 7 defective
5 1 7 defective

Box 2 is the only acceptable unit found in the sample. The sampling plan gives 3 and 4 as the Ac and Re numbers respectively. Since the Re number of 4 has been reached, the lot must be rejected.

Table 3: Destination inspection sampling plan
Units in lot Sample size-minimum number of units to be selected Eggs to be examined (60 eggs per unit) Destination tolerance - Grades A and B -
3% crack tolerance Table Note 8
Destination tolerance - Grades A and B -
7% tolerance all under-grades Table Note 8
2 120 3.6 8.4
26-50 3 180 5.4 12.6
51-90 4 240 7.2 16.8
91-150 5 300 9 21
151-280 8 480 14.4 33.6
281-500 13 780 23.4 54.6
501-1200 20 1200 36 84
1201-3200 32 1920 57.6 134.4
3201-10,000 50 3000 90 210

Table Notes

Table Note 8

The tolerances (3% and 7%) have been calculated out so that the values in the column are expressed as number of eggs.

Return to table note 8  referrer

The tolerances in Table 3 are based on the Canadian grade compendium: Volume 5 - Eggs. A sample, representing a lot, may have up to 10% total under-grades and still be considered acceptable. Of the 10% total under-grades, the first 3% (crack tolerance) is an allowance for cracks only. Any cracks in excess of 3% are added to all other under-grades and the total cannot exceed 7%. Note: the 7% does not include leakers and rejects.

Table 4: Pre-grade/ Nest Run Sampling Plan
Units in lot Sample size - minimum number of units to be selected Minimum number of eggs to be examined
0 - 25 2 120
26 - 50 3 180
51 - 90 4 240
91 - 150 5 300
151 - 280 8 480
281 - 500 13 780
501 - 1200 20 1200
1201 - 3200 32 1920
3201 - 10,000 50 3000

Appendix 2: Pre-grade and grade requirements table

Pre-grade and grade requirements table
Pre-grade (lot basis) Canada A Canada B Canada C Canada Nest Run
Weight n/a AJS - 70 g min
AELS - 63 g min
ALS - 56 g min
AMS - 49 g min
ASS - 42 g min
APW - less than 42 g
49 g minimum no requirements n/a
Albumen average Haugh Unit 67 and above reasonably firm no requirements no requirements n/a
Yolk n/a indistinct yolk outline
round and reasonably well centered
distinct yolk outline
moderately oblong
floats freely
slight degree of germ development
prominent yolk outline
definitely oblong
does not adhere to shell membrane
n/a
Air cell no more than 5% with air cells larger than 5 mm maximum 5 mm maximum 9 mm no requirements n/a
Blood or meat spots n/a not permitted not permitted maximum 3 mm in diameter n/a
Dirt no more than 5% with dirt (excluding yolk) between 160 mm2 and 1/3 of shell
no more than 2.5% with dirt (excluding yolk) on more than 1/3 of shell
not permitted not permitted not permitted maximum 5% where dirt is more than 160 mm2
Stains no more than 5% with stain covering 2 of shell maximum 3 stains
maximum total area 25 mm2
maximum total area 320 mm2 maximum total area 1/3 of shell no requirements
Shape roughness ridges maximum 10% normal or nearly normal in shape
may have rough areas and ridges other than heavy ridges
slightly abnormal
has rough areas and definite ridges
no requirements n/a
Cracks maximum 10% not permitted not permitted may be cracked, but not leaking maximum 10%
Leakers maximum 2.5% not permitted not permitted not permitted maximum 3% including rejects
Total maximum total 15% n/a n/a n/a maximum total 15%

Appendix 3: Haugh unit determination

The Ames Haugh Unit Micrometer is a precision instrument used for checking albumen height of eggs. It has a special two part dial which permits you to read the Haugh unit values directly.

  1. The dial face consists of two parts. The inner part is fixed. The outer part of the dial face is adjustable by turning the knurled rim of the Dial Indicator.
  2. The inner, fixed part of the dial has 3 segmented scales printed in black and reading in ounces per dozen (OZ/DOZ) at top of dial; in ounces per egg (OZ/EGG) at lower right of dial; and in grams per egg (GRAMS/EGG) at lower left of dial. The pointers or indices for these scales are small black triangles on the inner edge of the outer dial, overprinted on the red scale.
  3. The outer dial has two scales. One, printed in red, reads in tenths of a millimeter. The other, printed in black reads in Haugh units.
  4. The indicating hand follows the movement of the micrometer spindle as it is raised or lowered by turning the knurled knob at the top of the Indicator.

Note

Before measuring the albumen, always withdraw the spindle of the micrometer (counter-clockwise turn of the knob), then bring it down slowly upon the albumen to be measured by a clockwise turn of the knob.

Important

This instrument has been factory adjusted so the Indicating Hand aligns with the graduation representing 24 OZ/DOZ when the spindle tip makes contact with a plane, flat surface supporting the instrument. If, at some later time, the Indicating Hand points to some other graduation under these conditions, the set screw on the neck of the tripod should be loosened slightly and the Indicator re-positioned vertically to re-establish the previous Hand alignment. Then the set screw should be firmly tightened.

General procedure to determine Haugh units:

  1. Weigh eggs to be tested. For speed in operation, sort the eggs into groups of like weights. By grouping the eggs according to common weights, it is necessary to adjust the dial for weight differences only between the measurements taken for each group. Weight may be determined in ounces per dozen, (oz/doz), ounces per egg (oz/egg) or grams per egg (grams/egg), as the operator desires. The 3 scales on the inner part of the dial may be used interchangeably by using the index and scale desired.
  2. Set the index for the weight of the first group of eggs to be tested by twisting the knurled rim of the Indicator.
  3. Break out the first egg on a plane, flat surface.
  4. Retract the spindle of the micrometer by a counter-clockwise turn of the micrometer knob.
  5. Place the micrometer over the egg, being careful to place it so the legs do not pierce any part of the firm albumen envelope.
  6. By sliding the micrometer, position the spindle over the firm albumen about mid-way between the yolk and edge of the envelope and bring the stem down slowly by a clockwise turning of the Indicator knob. Watch the tip of the spindle and the albumen closely. The proper reading is obtained when the albumen appears to snap up to the specially designed tip of the spindle. Stop twisting the knob promptly when this occurs.
  7. Read the Haugh unit value directly from the position of the Indicating hand on the outermost scale (printed in black), each division of the black scale equals 1 Haugh unit.
  8. Wipe the spindle with a clean cloth or tissue after each use. Retract the spindle and the instrument is ready for use again.

The micrometer may also be used as an ordinary spherometer by placing the index marked set at 24 oz/doz and reading height of firm albumen (or of any other object placed on a plane surface) on the red scale. Each division of the red scale equals 0.1 mm.

Guidelines for Haugh Unit Measurement

  1. Comparable results can be obtained only if uniform procedures are used.
  2. The use of a breaking knife to break the shell is preferable, since blunt edges such as table edges may cause splintering of the shell with the possibility of puncturing the thick white. Care must be taken in using the breaking knife so that the thick white is not ruptured.
  3. At the time of breaking, the egg should be held as near to the glass as possible and the contents emptied very gently from the shell.
  4. When the envelope of thick white is firmly attached to the shell membrane (usually in the small end) rupture of the thick white can usually be prevented by slowly raising the half shell.
  5. A section of the shell may be left in contact if it does not interfere with the reading.
  6. Albumen heights should be measured immediately after breaking, therefore, break one egg at a time. A delay of a few minutes can make a significant difference in the Haugh unit reading.
  7. Check the micrometer before using. Set it on the glass and turn the spindle down until it touches the surface of the glass. The micrometer indicator should read zero. This should be repeated from time to time, to ensure that the micrometer is properly adjusted.
  8. The micrometer reading must be taken on a flat area on the surface of the widest expanse of the thick white.
  9. Eggs with very high albumen will not have a flat surface. In such cases, a point about halfway between the yolk and the edge of the widest expanse of thick white should be selected to measure the Haugh unit.
  10. Measurements should be taken so as to avoid measuring areas over air bubbles or chalaza.
  11. The spindle should be rolled down slowly until it just makes contact with the surface of the albumen. After the reading is measured, the spindle should be raised and cleaned before re-using.
  12. Albumen heights should not be recorded when the thick white has been mechanically ruptured or when the yolk membrane is ruptured from any cause.
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