Water Bath Heating Used to Decontaminate Shells in Australia


In previous months Australia has recorded cases of egg-borne infection with Salmonella Enteritidis (SE) and Salmonella Typhimurium (ST). The former pathogen, a Group-D serotype, is transmitted vertically to eggs by the trans-ovarial and trans-oviductal routes while non-Group D serotypes are associated with contamination of the shell during oviposition.


Research conducted in Australia demonstrated that low temperature water-bath immersion for ten minutes at 135F removes surface contamination. Although this is an effective procedure as confirmed by laboratory-scale studies, commercial application will be relatively expensive.  The approach is similar to the patented U.S. Davidson immersion process for pasteurizing eggs contaminated with internal SE.


Experience has shown that water-bath immersion is relatively expensive with respect to capital cost and the complexity of temperature control and recording systems. Batch processing is generally labor intensive and is associated with limitations on throughput.


In the U.S. shell eggs are subjected to a continuous washing process with an initial passage through a washer circulating a detergent sanitizer solution containing 100 to 150 ppm chlorine at a pH of 10 to 12 units. Commercial washers are operated over a range of 115F to 125F followed by a rinse at 130F to 140F, maintaining a 15F higher temperature in rinse water compared to the wash solution. Commercial packing in U.S. in-line plants approximates 400 to 600 cases of 30-dozen eggs per hour. The incorporation of washing in U.S. plants together with electronic crack detection to reject eggs with defective shells has eliminated egg-borne ST infection from product derived from plants operating under USDA inspection and SQF compliance.


The research and methodology for the immersion process was developed in response for a need to decontaminate shell eggs to be used in recipes calling for raw eggs.  The low-temperature process although removing ST will not inactivate SE within an egg and consumers in Australia will still be at risk. This especially the case in that Nation since a growing proportion of “chooks” producing table eggs are held on range.


If producers in Australia wish to market eggs with safety, in-shell pasteurization using a microwave system is recommended. For commercial food preparation and for recipes calling for liquid egg or albumen, pasteurized product should be used.