Dating back to the mid-to-late 20th century, chlorine was the most widely used antimicrobial chemical agent in US poultry processing.  However, peroxyacetic acid (PAA) has now gained in popularity as a replacement for chlorine. 

The shift toward PAA was gradual, at first, and primarily driven by its broad-spectrum effectiveness against a wide range of microorganisms, including bacteria such as Salmonella, E. coli and Campylobacter. 

Then in 2010, the Russian ban on "chlorinated" chicken imports, coupled with similar prohibitions in European countries, significantly accelerated the adoption of PAA over chlorine.

Despite the shift toward PAA, chlorine has not disappeared from use in US poultry processing plants. It continues to play an important role for pathogen intervention in the process water. Even the suppliers of PAA to poultry plants typically recommend the addition of chlorine for certain applications.  

Using only PAA, plants can obtain very favorable post-chill test results for whole birds, but considerably less so for parts. That is one of the reasons that most plants utilize a multi-hurdle strategy, including multiple dip tanks and more than one antimicrobial chemical. 

The cost of chlorine is less than that of PAA and it is the preferred second chemical in a multi-hurdle approach. Applications where chlorine is found to be particularly effective include evisceration lines, IOBW’s, further processing lines, belts, sinks, tote washers and even scalders and pickers. 

In order for chlorine to be in its most effective form, the pH of the water must be controlled throughout the entire process. A pH that is too low can be corrosive to equipment, so care must be taken not to bring the pH down below the corrosion limits of the equipment in use. However, the lower the pH the more effective the chlorine. A pH of 6.5 is the target for many poultry processing applications. (See the chart for the approximate relationship between pH and chlorine strength.) Chlorine is available to poultry plants in three different forms: chlorine gas (elemental chlorine), sodium hypochlorite (bleach), and calcium hypochlorite (typically in tablet form); each with its own advantages and disadvantages.

While chlorine gas is highly effective, the risks associated with a possible gaseous chlorine release, along with the requirements for specialized equipment and safety protocols, have led to most, if not all, poultry plants to no longer using the gaseous form. Alternatively, a number of plants use bleach, which they may pair with citric acid for pH control. By separately adding each component, operators achieve greater efficacy and find the process to be both effective and simple to execute. However, many operators say that the risk of spills, need for containment with two such highly concentrated liquids, and the movement of heavy drums are concerning. From a use and handling standpoint, they would prefer dry chemical products rather than liquids.  

Elemental chlorine, sodium hypochlorite and calcium hypochlorite tablets all have their place in poultry processing, depending on the particular application. Gas and bleach represent the largest production volumes, but for food processing Westlake, a major manufacturer of chlor/alkali products and derivatives, has seen tremendous growth in dry chlorine tablet systems as a replacement for the other two. More recently, sodium bisulfate tablet systems, which offer a safer alternative to citric acid for pH control are growing in use for food processing. 

The poultry industry is a dynamic one, having undergone numerous transformations with regard to food safety strategies and the chemicals used. Cetylpyridinium chloride (CPC), organic acids like citric and lactic acid, electrolyzed water, ozonated water, and trisodium phosphate (TSP) are among the other antimicrobials in use. However, the use of chlorine has a long and proven history in poultry processing, which endures today.