The Haugh unit is a measure of egg protein quality based on the height of its egg white (albumen). The test was introduced by Raymond Haugh in 1937 and is an important industry measure of egg quality next to other measures such as shell thickness and strength.

An egg is weighed, then broken onto a flat surface (breakout method), and a micrometer used to determine the height of the thick albumen (egg white) that immediately surrounds the yolk. The height, correlated with the weight, determines the Haugh unit, or HU, rating. The higher the number, the better the quality of the egg (fresher, higher quality eggs have thicker whites). Although the measurement determines the protein content and freshness of the egg, it does not measure other important nutrient contents such as the micronutrient or vitamins present in the egg.

Formula

The formula for calculating the Haugh unit is:

Where:

• HU = Haugh unit

• h = observed height of the albumen in millimeters

• w = weight of egg in grams

Haugh Index :

AA : 72 or more

A : 71 - 60

B : 59 - 31

C : 30 or less

Below are the USDA's terms describing egg white and its corresponding Haugh unit:

(a) Clear. A white that is free from discolorations or from any foreign bodies floating in it. (Prominent chalazas should not be confused with foreign bodies such as spots or blood clots.)

F.

F.

F.

• Excerpt from United States Department of Agriculture (USDA)

United States Standards, Grades, and Weight Classes for Shell Eggs, AMS 56, Effective July 20, 2000

References