The system for cryogenic egg cooling uses carbon dioxide gas to reduce the time required for cooling the eggs from days to minutes. As consumers become increasingly aware of food safety issues, one benefit of this new technology is a reduction in the risk of contracting Salmonella enteritidis from eggs.

A demonstration unit, known as CryoChill for Eggs, has been installed at Carolina Egg, a large egg processing operation. The equipment was developed by Praxair of Burr Ridge, Ill.

Dr. Ken Anderson, associate professor of poultry science, and Dr. Pat Curtis, professor of food science, developed the cryogenic egg-cooling system. Dr. Kevin Keener, assistant professor of food science, has proven that cryogenic cooling is very effective in controlling the growth of any Salmonella that may be present in eggs. The three faculty members, all specialists with the North Carolina Cooperative Extension Service, collaborated on the project with Dr. Donald Conner, Auburn University poultry scientist.

When eggs are rapidly cooled after laying, any microorganisms within the eggs become less resilient and are more easily killed during cooking. While the chance of contracting Salmonella from eating eggs is extremely remote, this system will reduce the possibility even further.

At the same time, it will extend the shelf life of domestic eggs, increasing opportunities for exporting eggs and enhancing the overall quality of eggs. The researchers have asked the U.S. Department of Agriculture and the U.S. Food and Drug Administration to approve a 60-day shelf life for eggs cooled by carbon dioxide gas. This would double the current 30-day shelf life allowed for eggs.

Using this new system, eggs leave the laying operation and pass through equipment for grading. Then, after a trip through the washer, the eggs pass through an 18-foot cooler filled with carbon dioxide gas at a constant temperature of minus 60 degrees Fahrenheit, before they are placed in cartons.

In the minutes it takes for the eggs to pass through the cooler, the eggs’ internal temperature can be reduced from 94 degrees F to 45 degrees F, the optimal temperature required by the USDA. Using traditional refrigeration to cool the eggs, it takes seven to 10 days to reduce internal egg temperature to 45 degrees. Curtis said that cryogenic cooling should help producers save on conventional refrigeration costs because eggs will enter the refrigerators at a much lower temperature.

Studies showed that eggs cooled quickly with carbon dioxide gas had no growth in microbial content for up to 10 weeks. By contrast, eggs cooled through traditional refrigeration showed microbial growth six times greater at eight weeks than the cryogenically cooled eggs.

Anderson and Curtis have been experimenting with new techniques for cooling eggs for a number of years. But only recently, with increased concern over Salmonella in eggs, has the industry become interested in commercializing new technologies for cooling eggs faster.

The researchers have tested methods of cryogenically cooling eggs with liquid and gaseous nitrogen, as well as carbon dioxide. They found that carbon dioxide worked better in preserving the quality of eggs because carbon dioxide occurs naturally in eggs.

"Most people think that the highest quality egg you can get is when it is first laid. But that’s not true when compared with carbon dioxide-cooled eggs. The benefits seem to be long-term," Anderson said.

"We are trying to make sure that, from egg production through the grocery store, there is no possibility of any organisms reproducing."

—Natalie Hampton