Agriculture and Food 7–12 · Years 9–10

Egg quality: Haugh units, air cell depth and storage temperature

Animal Production 1

Practical, model not builtLow risk

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The idea

As an egg ages its thick white thins and its air cell deepens, so measuring albumen height against egg mass gives the Haugh unit, the interior-quality measure used in United States grading and in egg research. Australian egg quality assurance instead runs under Egg Standards of Australia, a certification based on HACCP principles that sets no albumen grade, so the class measures interior quality by one scheme and compares it with the way the Australian industry assures quality.

What you need

24 eggs of one brand and pack date (or school farm eggs of known lay date)
refrigerator at 4 °C and a room-temperature cupboard for 7 days of storage
insulated box (esky) with a lid and a thermometer lying among the eggs, for holding them in the 7.2 to 15.6 °C band before testing
balance reading to 0.1 g
albumen height micrometer (tripod gauge) or a vernier depth gauge on a bridge
level glass plate on a stand, egg-breaking knife, candler and a ruler for air cell depth
thermometer, paper towel, disinfectant for the bench

How to do it

Store 12 eggs at 4 °C and 12 at room temperature for 7 days.
Bring all eggs to between 7.2 and 15.6 °C before testing, the range the USDA grading manual specifies for Haugh units, and record the temperature. Neither store sits in that band: the refrigerator at 4 °C is below it and the room-temperature cupboard above it. Put both groups into the insulated box with a thermometer among them, and hold them there until the thermometer reads inside the band and stops moving, then test both groups out of the box so their internal temperatures are uniform, which the manual also requires. Do not record a Haugh unit for an egg tested outside the band.
Candle each egg and measure the depth of the air cell.
Weigh the egg, break it gently onto the level glass (one egg at a time) and measure the height of the thick white immediately, at a flat spot halfway between the yolk and the edge, avoiding chalazae and bubbles.
Calculate the Haugh unit value with the model and assign the USDA albumen grade.
Compare mean Haugh units and air cell depth for the two storage treatments.

What you should see

A 60.0 g egg with a 7.0 mm thick-white height scores 83.7 Haugh units (AA); with 4.0 mm it scores 58.7 (B). The USDA grades are AA at 72 or more, A from 60 to below 72 and B below 60, and air cells of 1/8 inch (3.2 mm) or less for AA and 3/16 inch (4.8 mm) or less for A. These are United States retail grades: Egg Standards of Australia, the Australian industry quality assurance programme, is based on HACCP principles and sets no albumen grade or Haugh unit, so the class reports the measurement in USDA terms and then says what an Australian grading and packing floor assures instead. Eggs stored at room temperature for the week are expected to score fewer Haugh units and have deeper air cells than those kept at 4 °C. Shell colour plays no part. The learner knows it worked when every egg was tested from the insulated box inside the 7.2 to 15.6 °C band, repeat height readings on one egg agree to the gauge's resolution, and the two storage groups separate.

What changes

What you change: storage temperature for 7 days (4 °C or room temperature)
What you measure: Haugh units, air cell depth (mm)
What you keep the same: same brand and pack date
egg temperature at testing
measuring position
time from breaking to measuring

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

Brown eggs are better quality than white eggs.
A shell protects an egg, so storage temperature does not matter.
A bigger egg always has better quality.
A Haugh unit grade is what Australian eggs are sold on.

Safety card

Low riskLearners carry it out

Hazards

Salmonella from raw egg on hands and surfaces
breakage of the glass plate

Controls

wash hands and disinfect the bench afterwards
raw egg is not tasted
glass plate on a stable stand

Note

Food handling follows the FSANZ food safety standards (Standard 3.2.2) as explained on the FSANZ food temperature and thermometers page; check class allergy and anaphylaxis records before any food is prepared; the Food Technology Years 7–10 Syllabus reminds teachers that food allergies can cause anaphylaxis.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Agricultural Technology Years 7–10 Syllabus (2019)AG5-7
Food Technology Years 7–10 Syllabus (2019)FT5-3 FT5-4
Agriculture Technology 7–10 Syllabus (2024), new syllabus, implementation from 2027AGT5-PRA-01
Australian Curriculum v9AC9TDE10K04AC9TDE10K05

Sources

The pages the author read to write this activity.

All Concept Studio activities