Reduction of Salmonella on poultry during processing requires a multi-hurdle approach. The following article details interventions that can be used during processing to lower Salmonella progressively as the carcass progresses down the line.

Pre-scald bird brushes remove feces from birds prior to entering the scalder. One company used this technique to decrease the amount of fecal material going into the scalder by approximately 90%.

The scalder is one of the most important areas in the processing plant in which cross-contamination with Salmonella can occur. Most scalders are not set up to be truly counter-current. Fresh water should not be added to the middle of the tank. There is a common adage that goes, “dilution is the solution to pollution,” and it applies in this case.

An ideal scalder set-up is depicted in Figure 1.

If organic material from the scalder makes it to the chiller, then oxidative sanitizers, such as chlorine, will have little effect on bacterial concentrations later on.

Controlling cross-contamination in the scalder  

Most older scalders are like a bath (Photo 1), as opposed to having a counter-current flow. This counter-current flow has the effect of washing the chickens, much as a fast moving river would wash dirt from a person better than would a bathtub.

If the surface of the carcass is contaminated with Salmonella in the scalder as a result of the bacteria being transferred from bird to bird, another problem may occur in picking.

Addition of chemicals to the scalder and lowering temperatures   

Chlorine should not be used in scalders because it is immediately deactivated by the organic load in the scalder and can gas off. Strong acids can greatly benefit processors when used during scalding because they accomplish the following things:

  • Decrease the force needed to pick birds, reducing wing damage
  • Decrease Salmonella levels on the birds
  • Allow processors to decrease scalder temperatures, increasing yield
  • Decrease breast striping due to over scald
  • Increase yield on final chilled carcasses
  • Decrease the amount of energy needed to scald chickens
  • Controlling cross-contamination in the pickers

The pickers present a serious problem for processors when it comes to cross-contamination. Figure 2 shows how Salmonella prevalence may be increased during picking.
Strong acids have been shown to be effective for lowering Salmonella on birds during picking and reducing cross-contamination. However, the poultry industry is not accustomed to paying for chemicals in the front of the plant. As new Salmonella regulations are implemented by USDA, the industry may begin using chemical hurdles at the front of the plant, even though they are resistant because of the cost.

Inside/outside bird washers (IOBW)   

Companies generally use chlorine in IOBW systems. However, a comprehensive research study conducted by Northcutt et al. (2005) of the USDA-ARS clearly demonstrated that adding chlorine to the IOBW has absolutely no impact on aerobic plate counts, Escherichia coli counts, Salmonella prevalence or Campylobacter counts on carcasses. These data correlate well with numerous biomapping studies. Chlorine is not able to penetrate the organic material and interact with the bacteria. Therefore, little or no effect is observed.

Online reprocessing systems   

The purpose of OLR systems is not to reduce Salmonella. The USDA-Food Safety and Inspection Service (FSIS) views the OLR as a process intended to make carcasses that would otherwise have to be reprocessed by hand (because they have fecal material or ingesta on them) microbiologically equivalent to those carcasses that do not have any fecal material or ingesta on them.

The following are chemicals used by the poultry industry (94 plants responded to a survey out of approximately 247 in the U.S.) for OLR purposes and the percentage of companies using each chemistry:

  • Acidified sodium chlorite (Sanova - 33%)
  • Trisodium phosphate (Rhodia – 24%)
  • Chlorine dioxide (numerous companies – 15%)
  • Hypochlorous acid (Zentox and TOMCO – 9%)
  • Organic acids (6%)
  • Peracetic acid (FMC 323 or Parasafe and Inspexx 100 - 5%)
  • Cetylpyridinium chloride (Safefoods Cecure - 3%)
  • SynerX (citric acid and HCL – 1%)
  • Bromine (BromitizeTM – 1%)
  • Sodium metasilicate (AvguardXP - 1%)
  • Electrolyzed oxidative water (EAU – 1%)

Chemicals not mentioned in the survey include Zentox monochloramine and SteriFx (FreshFx) which was included with organic acids, but contains mostly inorganic acid.

Strong acids and mixtures   

Since the time of this survey, some companies have begun to use strong acids or mixtures of organic/inorganic acids for OLR purposes.

Unfortunately, there are still no magic bullets for use with OLR systems. The short contact time and methods of application (generally a spray) make it very difficult for chemicals to eliminate Salmonella during this step.


We have observed reductions in Salmonella prevalence of 0% to 90% using various chemistries. It is also possible to see this type of variation from plant to plant using an individual chemical. This is because plants and incoming loads vary tremendously from plant to plant. Thus, it is important to select the appropriate type of sanitizer based on an individual plant setup.

Disinfection during chilling   

More bacterial reduction (both numbers and prevalence) can be accomplished in a properly balanced chiller than anywhere else in the processing plant. As with the scalder, the pH, temperature, flow rate, flow direction, chlorine concentration and concentration of organic material (digesta, fat, blood) is crucial in order for the chlorine in the chiller to do its job. The pH should be below 6.5, the flow rate should be high, and the flow direction should be counter-current.

The most effective methods for controlling the pH of chill water include addition of carbon dioxide gas to the tubes normally used for air agitation (90% of the industry uses this method according to a U.S. Poultry and Egg Association survey), the addition of citric acid or other inorganic acids (10% of the industry uses this according to the survey) or the addition of sodium acid sulfate to the water.

Organic loading in the chiller   

The organic material in the chiller is generally determined by the following factors: the flow rate (amount of fresh make-up water), flow direction (should be counter-current), the use of pre-scald bird brushes and the cleanliness of the scalder, the temperature of the scalder, the number of high pressure carcass sprays used on the line prior to the chiller, and the number of chill tanks (more tanks equals less organics). Excessive organic material (blood, digesta, fat, protein) in the chiller will result in less chlorine being available to kill bacteria, as it will be bound up and rendered useless by the organic material.

Many of the chillers in the industry are more like a bath than a river. The water is stagnant and organic material builds up during the shift (Photo 3). Also, fat builds up on the chiller paddles and sides of the chiller (Photo 4). This allows for Salmonella to be encased in the fat, offering it protection from the sanitizers used in the chiller.

Suggestions for maintaining a balanced chiller include:

  1. Maintain proper water flow direction (counter-current)
  2. Maintain proper water pH (below 6.5)
  3. Maintain proper chlorine level
  4. Maintain water temperature below 40 F

Addition of fresh water to chiller   

A properly operating chiller should have a visible gradient such that the water at the chiller exit is significantly cleaner than the water at the entrance. This is accomplished by adding all of the fresh water input and newly added chlorine directly to the exit end of the chiller as close to the exit paddles as possible. This will result in a “clean space” near the exit end of the chiller. In this space, chlorine will be able to act against bacteria, similar to the way a post-chill dip tank works. The ideal chiller setup is depicted in Figure 3.

Chemicals in the chiller   

The chemicals used in the U.S. for chiller applications and the percentage of plants that use them include hypochlorous acid (72%), peracetic acid (18%), chlorine dioxide (8%), bromine (1%) and monochloramine (1%) (Krushinskie, 2006 survey). Other chemicals not listed in the survey that have been used in the industry include sodium acid sulfate and electrolyzed oxidative water. These chemicals all have advantages and disadvantages associated with their use. Overall, the chiller, if operated properly can be the most significant intervention step for controlling Salmonella prevalence on broiler carcasses.

Post-chill dips and sprays  

Poultry processors are employing the “hurdle hypothesis” to reduce Salmonella at different locations throughout the plant. The “hurdle hypothesis” is the premise that the more hurdles (i.e. interventions) that are employed against Salmonella, the less likely it is that Salmonella cells will be able to survive until the end of the process. As a final intervention and hurdle, companies are now using post-chill dips or sprays.

Post-chill systems are advantageous in that the chickens are as clean as they will be throughout the process and the ability of any given chemical to contact bacteria on the surface of the skin without interference from organic material is highest at this point.

Some of the post-chill chemicals used include acidified sodium chlorite (Sanova), hypochlorous acid, peracetic acid (FMC 323 or Parasafe and Inspexx 100), a mixture of hydrochloric, citric, and phosphoric acid (FreshFx), chlorine dioxide (multiple companies), and electrolyzed oxidative acidic water (EAU) to name a few.

Post-chill application may be by tank dipping or spraying. The dip tanks used for these applications generally vary from small 50- to 100-gallon tanks to much larger (5,000- to 10,000-gallon) pre-chiller type tanks. Likewise, the contact time used by these poultry companies varies from eight seconds to 30 minutes. The spray systems are generally similar to those used for online reprocessing.

Combinations of interventions   

Overall, the companies are achieving success using post-chill dips or sprays and are finding that the interventions throughout the plant, combined with a post-chill dip system can be effective for lowering Salmonella and other bacteria to acceptable levels. 

Krushinskie, E., 2006.
Northcutt, J.K., D.P. Smith, M.T. Musgrove, K.D. Ingram, and A. Hinton, Jr., 2005. Microbiological impact of spray washing broiler carcasses using different chlorine concentrations and water temperatures. Poultry Science 84:1648-1652.