Salmonella levels on poultry can vary greatly depending on time of year, region, flock and environment. Research has shown that when 3 percent to 4 percent of birds entering a plant tested positive for salmonella, 20 percent to 35 percent tested positive after processing. Thus, cross-contamination is one hurdle to overcome in reducing salmonella. In order to determine which steps pose the greatest risks, microbial testing and data analysis (biomapping) can be used to determine which farms are likely salmonella-positive and what processing steps pose the greatest cross-contamination problems.

Multiple Intervention Strategies Needed

To adequately address salmonella throughout processing, multiple antimicrobial intervention strategies should be implemented. Strategies include physical and chemical interventions or a combination of the two. Good environmental stewardship would suggest that chemical use be minimized by implementing further physical intervention strategies. Application of these strategies should begin early in the process. Some of the first areas to consider are flock scheduling and cooling sheds.

Flock Scheduling.  In facilites where biomapping is employed, salmonella can be tracked to allow identification of positive farms. Flocks from farms thought to be salmonella-positive should be processed towards the end of a shift to prevent cross-contamination that could occur if the birds are processed earlier.

Cooling Sheds.  Since higher moisture promotes bacterial recovery, cooling sheds should be be examined. During the summer, misting often is used as way to help keep birds cool. Providing too much moisture can increase the spread of bacteria and may have a negative effect on the birds' ability to dissipate heat.

Water Quality.  Water quality can affect antimicrobials as well as functional ingredients used throughout processing. Specifically, water hardness, pH and mineral content can alter the activity of antimicrobials. For instance, water with a high pH will render chlorine ineffective. Water quality needs to be monitored so appropriate adjustments can be made.

Scalding, Picking And Evisceration

Brush scrubbers physically remove foreign material and excreta from birds prior to the scalder. Chemical rinses, generally hypochlorous acid, can be added to increase the effectiveness of this step. While the scalder is thought to reduce bacterial loads because of its high temperatures, other factors can limit its effectiveness. Factors that affect the antimicrobial capacity of the scalder include the level of organic load, scalder configuration, water flow rate and counter-current flow, water pH and temperature. High organic loads will act as a buffer in the chiller water, and salmonella grows at pH of 6.5- 7.5. Using scrubber brushes and rinses prior to birds entering the scalder will reduce the organic load.

Scalder additives can be used to adjust scalder pH to above 9 or below 4.5 as a means of preventing salmonella growth. Organic acids such as acetic acid have been used to lower the scalder pH; sodium hydroxide (NaOH) has been used to raise pH. While acetic acid can be effective, it can cause a vinegar smell. Acetic acid has been shown to be effective as low as 0.1 percent, while NaOH is effective at 1 percent.

During experiments with alkaline additives, the scalder water was cleaner (less solids) because solids seemed to fall to the bottom, and birds appeared whiter and cleaner. More importantly, salmonella and campylobacter were destroyed when carcasses inoculated with these bacteria were processed through the scalder containing the alkaline additive (Figure 1).

Scalder configuration  is also important. Many facilities have multi-stage scalding systems with a counter-current configuration. This allows birds to move towards cleaner water upon exiting the scalder. Maintaining a high water flow rate helps to dilute organic material and bacteria.

Another factor influencing bacteria reduction in the scalder is the water temperature. While most facilities use a hard scald process (~132°-136° F), some use a lower temperature or soft scald process (~120°-125° F).

Residual Salmonella Heidelberg was found in a facility using a soft scald process. As it turns out, S. Heidelberg is a little more heat stable than some other salmonella serotypes. Since the facility had implemented a biomapping program where various sites in the plant were tested, it could be determined that the S. Heidelberg was not effectively destroyed by the scald temperature or removed by cleaning and sanitizing. As a result, changes were made in the sanitary standard operating procedures to address the residual issue. Further analysis helped to identify the farm where S. Heidelberg had originated. A physical process implemented at this step was to increase the scalder temperatures to 165° F during breaks or shift changes and then bringing it back down prior to start-up. The higher temperature helped destroy bacteria that may not have been destroyed by the original scalding temperatures. While this physical step is very effective, it warrants close attention to make sure scald temperatures are correct before resuming processing.

Picking.  During processing, the microbial load on picking fingers increases over time, and wear and tear can produce cracks and crevices. Bacteria may not easily be removed during cleaning and sanitation; therefore, picking fingers should be checked and replaced regularly. In addition to routine maintenance, picking fingers should be effectively cleaned and sanitized daily.

During picking, chlorine sprays may be used to control bacterial counts; however, care must be taken when using chemicals because these may damage the picking fingers. Organic acids, such as acetic acid, are effective, but the smell could be a factor. Washes, pre- and post-picking, have not shown to have consistent results on the final bacterial load on poultry carcasses, but they may provide an overall dilution effect. Generally, when carcasses are rinsed post-pick, the chemical most typically used is chlorine at levels of 20-30 ppm. Other antimicrobials can be used as well, especially if they are used elsewhere and the plant configuration allows them to be pumped to various areas.

Evisceration.  Best practices include optimizing feed withdrawal so the intestines are cleared but not so fragile as to break during evisceration. Short withdrawal times have been shown to increase fecal contamination on processed carcasses, but longer times (>12 hours) can cause the intestines to be more prone to rupturing due to fragility.


Studies have shown that contamination of the crop with salmonella and campylobacter increases during preslaughter feed withdrawal, likely due to birds consuming pathogen-contaminated litter. To optimize feed withdrawal from a food safety standpoint, it is important to minimize litter consumption while meeting the "zero tolerance" for fecal contamination on carcasses at the plant. Generally, eight hours is recommended as an optimal feed withdrawal time to help meet the food safety criteria. Feed withdrawal may need to be further optimized based on the size of the birds. Bigger birds need more time for gut clearance than smaller birds.

Equipment also should be properly adjusted and effectively cleaned and sanitized. Disinfectant rinses need to be checked to make sure the chemical levels, spray pressure and distribution are correct.

Bird Washers And Rinse Cabinets

Rinse cabinets may be found at multiple locations throughout the plant. Rinse cabinets used for external bird rinses are often located at pre-scalding, picking and post-picking. Inside/outside bird washers (IOBW) are used after evisceration or prior to chilling.

Antimicrobials used may include acidified sodium chlorite, trisodium phosphate, peroxyacetic acid, chlorine dioxide, hypochlorous acid (20-30 ppm), organic acids and cetylpyridinium chloride. Acidified sodium chlorite (Sanova, 500 to 1,200 ppm) is commonly used. Trisodium phosphate is best not used prior to the chiller because it may raise chiller pH to above 9, and if chlorine is being used it will not form hypochlorous acid, which is the antimicrobial.

Antimicrobials applied in spray rinse cabinets may provide inconsistent results because of contact time, concentration of the antimicrobial used, bird coverage (distribution) and spray pressure. Equipment operations that should be checked include spray nozzle function, water pressure (nozzle) and spray coverage, which should be optimized with the line speed for adequate contact time.

Physical And Chemical Interventions In The Chiller

Several factors influence the effectiveness of the immersion chiller, including water temperature, water pH, level of organic material present, water flow rate, water counter current flow, water jet pumps (level of agitation), antimicrobial application and the use of automated antimicrobial control systems. Chiller water temperature should be maintained below 40 F.

During chilling, both physical and chemical antimicrobial interventions can be used. Physical interventions include using water jet agitation systems as opposed to the traditional air agitation. Morris and Associates manufactures a water jet system, called the JetBird system, which increases chilling efficiency (temperature reduction/time), helps prevent piling in the chiller and improves contact and overall effectiveness of antimicrobials in the chiller. Additional physical interventions include maintaining a counter-current water flow, and a high flow rate (up to 1 gallon per bird) which helps reduce organic load as well as increases the washing effect and temperature-reducing capability of the chiller.

Chemical interventions include use of approved antimicrobials, the most widely used of which is chlorine. When using chlorine in the chiller (20-50 ppm), the pH should be optimized so that hypochlorous acid is formed and chlorine is maintained at the desired level, usually 30 to 40 ppm free chlorine. Adjusting chiller water pH to 5.5 to 6.0 helps to insure that hypochlorous acid is formed. If the pH of the water in the chiller is above 7.0, levels of hypochlorous acid decline, as does chlorine's effectiveness as an antimicrobial. Typically, CO2 or citric acid is used to reduce chiller pH. In addition to pH, levels of organic material, particularly when high, reduce the level of free chlorine available. Organic material can be reduced by including a pre-rinse cabinet prior to the chiller, increasing the rate of water flow, maintaining counter-current flow and managing scalder temperatures to prevent fats from being liquefied and released.

Peracetic Acid And Other Antimicrobials

Other antimicrobials used in the chiller include peracetic acid, chlorine dioxide, bromine and monochloramine. Any antimicrobial used should be validated for effectiveness and tested to determine the optimal concentration necessary to achieve the desired bacterial reduction without negatively altering product quality. One validated product is Spectrum (FMC), which is a peracetic acid product. In a commercial validation trial, peracetic acid (85 ppm) reduced salmonella by 90 percent; whereas chlorine reduced salmonella by 56 percent (Figure 2). During the trial, it was evident that using automated controlling and monitoring systems is a major factor in maintaining antimicrobials at the desired level to maximize their overall benefit.

Chlorine's effectiveness as an antimicrobial is improved with automated monitoring systems that measure chlorine activity and pH. With such systems, it is necessary to monitor and adjust pH as well. One such system (Morris and Associates) monitors chlorine and pH levels, and electronic pump(s) deliver chlorine and acid to the chiller. Oxidation Reduction Potential (ORP) and pH sensors are used. ORP sensors measure oxidative capacity as voltage. Since chlorine is a strong oxidizing agent, the voltage increases as free chlorine levels increase. Such systems combined with electronic controllers can be effective in maintaining the activity of the antimicrobial and managing the chiller chemistry.

Finishing Chillers

Finishing chillers can also be beneficial in allowing antimicrobials to be used on the chilled carcasses. The antimicrobial can be applied with a water jet system increasing overall effectiveness and reducing the amount of antimicrobial needed.

Managing food safety is a challenge, but significant improvements can be achieved by using a multi-systems approach. While this article describes some of the best practices and technologies available, the antimicrobial interventions chosen for individual plants should be validated.