The importance of egg quality
As a natural product, all eggs are not equal and need to be routinely checked for quality to meet the specifications being increasingly demanded by today's quality conscious retailers.
Most retailers impose on their suppliers a specification that all eggs should meet. This usually embraces a range of quality characteristics, such as shell colour, Haugh Unit (HU) and yolk colour, as well as checks on packaging, barcodes, print colours and eggs being packed correctly, with the labels placed in the correct position.
One of the primary egg quality traits most frequently measured is albumen quality. Measured in millimetres (the higher the reading the better the quality). This measurement is a very efficient method of determining the quality and freshness of eggs.
The albumen thins as an egg ages because the protein in the eggs changes in character over time. - that's why fresh eggs sit up tall and firm and why stale or older eggs spread out and run all over a flat surface when they are broken out.
The Haugh Unit
In the 1930's, an American researcher, Dr R R Haugh, introduced a formula that is still used internationally as the definitive method of defining true egg quality and freshness. This formula takes into account egg weight in grams and albumen height in millimetres and provides - rounded up to whole numbers - a range of HU values from single figures in extremely poor quality eggs to over 100 plus in very good quality fresh eggs.
The HU calculation is commercially essential where eggs from different flocks and of different sizes/ages/breeds are tested.
Click here for a guide to quality by Haugh Unit.
Haugh Unit versus air cell
Whilst in many countries the air cell is still used as the statutory measurement to define the age of an egg, it should not be regarded as a method of guaranteeing egg quality - it is often possible to have an air cell within legal tolerances yet have the HU in the poor/unacceptable categories.
This is why many retailers have been very specific in writing into their product specifications HU levels usually in excess of 70.
The air cell height increases with age through loss of moisture. However long before the air cell reaches the point where the egg changes its quality grade, the true consumer quality can already have deteriorated. The speed of deterioration is dramatically affected by the storage temperature and age of the egg.