The Microbiology of Counterflow Scalding Systems

Authors: Cason Jr, John

Submitted to: Georgia Poultry Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 9/26/2006
Publication Date: 9/27/2006
Citation: Cason Jr, J.A. 2006. The Microbiology of Counterflow Scalding Systems. Georgia Poultry Conference Proceedings. p. 53-56.

Interpretive Summary: Scalding birds to make it easier to remove feathers has been done for thousands of years, long before anyone knew about the possibility that dirty water might contaminate food with dangerous bacteria. Multiple-tank scalders, where water flows in the direction opposite to movement of carcasses, reduce numbers of bacteria in the scald water. Numbers of bacteria dying in the hot water eventually equal the number of bacteria entering on new carcasses, so the number of bacteria in scald water reaches a limit. Although numbers of bacteria suspended in water in multiple-tank scalders can be predicted successfully with a computer program, it is still not possible to predict how bacteria will move between the feathers, carcass, and water.

Technical Abstract: For most of the thousands of years that humans have used scalding to make it easier to remove feathers from birds, no one knew about the microbiological implications of scalding. The hot water in scald tanks kills many bacteria, but scalding multiple birds in the same tank gives surviving bacteria an opportunity to transfer between carcasses. In multiple-tank, counterflow scalders (where water flows in the direction opposite to movement of carcasses), a decline in numbers and incidence of bacteria in successive tanks has been reported in many studies. Multiple-tank scalders clean up scald water by preventing the most contaminated water in the first tank from mixing freely and spreading throughout the entire volume of scald water in the other tanks, as would happen in a single tank with equivalent total volume of water. Bacteria in a scald tank may come from thousands of different carcasses. A plateau in the numbers of bacteria in scald tanks occurs when the number of dying bacteria is approximately equal to the number of bacteria entering on incoming carcasses. Although it appears that numbers of bacteria suspended in water in multiple-tank scalders can be modeled successfully, it is still not possible to predict how bacteria will move between the feathers and carcass.