The Haugh unit is a measure of eggprotein quality based on the height of its egg white. 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, and a micrometer used to determine the height of the thick albumen 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. 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: Clear. A white that is free from discolorations or from any foreign bodies floating in it. Firm. A white that is sufficiently thick or viscous to prevent the yolk outline from being more than slightly defined or indistinctly indicated when the egg is twirled. With respect to a broken-out egg, a firm white has a Haugh unit value of 72 or higher when measured at a temperature between 45F and 60F. Reasonably firm. A white that is somewhat less thick or viscous than a firm white. A reasonably firm white permits the yolk to approach the shell more closely which results in a fairly well defined yolk outline when the egg is twirled. With respect to a broken-out egg, a reasonably firm white has a Haugh unit value of 60 up to, but not including, 72 when measured at a temperature between 45F and 60F. Weak and watery. A white that is weak, thin, and generally lacking in viscosity. A weak and watery white permits the yolk to approach the shell closely, thus causing the yolk outline to appear plainly visible and dark when the egg is twirled. With respect to a broken-out egg, a weak and watery white has a Haugh unit value lower than 60 when measured at a temperature between 45F and 60F.
