In order to reduce core temperatures and control microbial activity on processed poultry, carcasses are currently immersed in specialized chillers. These large tanks are typically filled with chilled water that cools the carcasses to temperatures needed to inhibit pathogen growth, which are typically around 4°C. The process, however, uses a considerable amount of water and energy along with the additional cost of chemical disinfectants. Researchers at the Georgia Tech Research Institute (GTRI) are exploring the use of ice slurry as an alternative chilling medium.
Ice slurry contains tiny ice crystals that are formed by mixing water with a freezing point depressant, such as salt. The slurry is produced by a specialized mechanical means of forming or cutting/scraping. The result is a “two-phase” mixture of micro-sized ice and water with excellent chilling ability. The GTRI team, having learned of the fishing industry’s use of ice slurry as a coolant preservative, thought the same could hold true for poultry processing operations.
“Ice slurry will give you more cooling capacity per unit mass of water, so the assumption is that if you use ice slurry you can reduce the amount of water needed and/or provide a quicker chill,” explains Dr. Comas Haynes, GTRI principal research engineer and project director.
The team is working with several industrial and government partners: an ice slurry machine is on loan from Ice Synergy Inc.; local poultry companies have donated carcasses for testing in support of GTRI’s Agricultural Technology Research Program; the USDA’s Russell Research Center has provided a laboratory-scale auger chiller; and representatives from Southern Company Services are providing sponsorship and technical advice in regard to electricity/energy savings.
Initial experiments were performed to benchmark the ice slurry’s cooling capacity. One set of experiments used the ice slurry, while another set used conventional chilled water. The team found carcass core temperatures decreased from 40°C to 4°C in 45 minutes, and with an average chilling medium temperature of -1°C with the slurry — as opposed to a significantly slower and more limited decrease in carcass core temperatures with chilled water, notes Haynes.
The ability to pump slurry throughout a facility also adds to its attractiveness when compared with conventional ice, which can have sharp edges. “Some people even call it liquid ice,” says Haynes, referring to the ice slurry. “Even though technically it is ice, it is such a tiny, fine grain that it can literally be pumped like water.”
This would be a benefit over the current process in terms of handling and transportation. With an ice slurry machine and holding tank, the slurry can be made on-site and then easily pumped to the existing chiller. In addition, the ice slurry can be made during off-peak hours and stored for later use, helping to achieve energy efficiency and lowering electricity costs.
The team is currently investigating the slurry’s potential as an antimicrobial aid. Experiments are underway with one set of Salmonella-inoculated carcasses and one set without. Results are pending.
Haynes hypothesizes that the ice slurry’s grain may act as a “scrubber” along the carcasses’ skin, helping to loosen potential microbes directly into the chiller’s water, hastening disinfection and possibly reducing the amount of chemical disinfectant needed.
“Our ultimate goal is to develop a system-of-systems approach to poultry chilling,” says Haynes. This includes establishing an ice slurry system as a thermomechanical innovation for food safety — thermal in its capacity for rapid and colder chilling and mechanical for its hypothesized “scrubber” antimicrobial effect.
Haynes believes that considering an ice slurry system for existing or future plant operations that is optimized for specific poultry processing applications like chilling and sanitation could be a winning proposition.