Submitted to: National Egg Quality School Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/5/2011
Publication Date: 5/16/2011
Citation: Jones, D.R. 2011. Understanding the Haugh Unit. Proceedings of the National Egg Quality School.V1:30-31.
Technical Abstract: Rapidly determining shell egg quality in an objective manner is not an easy task. Candling is most often utilized as a quick method for assessing egg quality in a non-destructive manner, but it is a highly subjective method. As you have experienced this week, when candling, it is almost impossible for multiple people to grade an egg exactly the same. Ultimately, perceived physical egg quality is an interaction of the albumen and yolk stability (centering of the yolk in the thick albumen). Raymond Haugh developed the Haugh unit in 1937. It has become the most widely used measurement of albumen or interior egg quality and by many is considered to be the “gold standard” of interior egg quality determination. The Haugh unit is a correlation between egg weight and the height of the thick albumen. The calculation (which can be cumbersome) is weighted for a 56.7g (2 oz) egg (large size). Several authors have argued that the calculation is inaccurate for eggs other than size large. (Please contact me if you would like copies of these articles.) Haugh unit measurement is a destructive test and is generally conducted on a grading sample of eggs within a lot. The USDA Agriculture Marketing Service (AMS) has accepted the Haugh unit as a valid and reliable method for determining interior egg quality. USDA grade standards have been established for Haugh unit readings (Table 1) and may be found in AMS 56.210 (http://www.ams.usda.gov/AMSv1.0/getfile?dDocName=STELDEV3004376). These grade/score combinations are not the same for all countries. Therefore, if you export product, you need to investigate requirements for individual countries. Table 1. Haugh unit score and USDA grade equivalents. Grade Haugh unit score AA = 72 A 72 > score = 60 B < 60 Traditionally, a glass-topped break-out table and micrometer were utilized. (Pictures can be found at: http://www.ams.usda.gov/AMSv1.0/getfile?dDocName=STELDEV3004502.) All numbers were logged and calculations had to be performed separately. There are also Haugh unit tools which use an internal calculator to calculate the Haugh unit score as you measure albumen height. The most modern devices are electronic and connected to computers to instantly record the Haugh unit value for the egg. There are two such devices currently on the market, one from Europe and another from Japan. Please contact me if you would like to obtain additional information on these units. There are differences in the capabilities of each of these devices, so one may be better suited to your needs than the other. The units are pricey and may only be economically feasible when large numbers of eggs are being examined. When performing a test, care should be taken when placing the micrometer over the egg. If the micrometer is too close to the yolk or near the chalazae, an inaccurately high Haugh unit value may be calculated. A general rule of thumb, read the thick albumen height at least 1 cm from the yolk. In very fresh eggs this may not be possible. Under these circumstances, place the micrometer half the distance between the yolk and edge of the thick albumen. A break-out table is often utilized for Haugh unit measurements to allow the person conducting the test to identify when the micrometer has touched the thick albumen surface. An accurate measurement allows for the micrometer to just make contact with the thick albumen. Whatever the surface being utilized during analysis, it should be flat, smooth, and level to prevent difficulties in achieving accurate readings. According to AMS, all Haugh unit evaluations should be performed on eggs with internal temperatures of 45-60F (7-16C). A special note, for comparison, all eggs should have similar internal temperatures since temperature has a direct effect on albumen quality. Micrometers or other devices utilized for Haugh unit measurement should be