Food Safety for Dairy Processors

Win the war against listeria

June 12, 2014
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Let’s be honest. Dairy plants are a war zone when it comes to the battle against foodborne illnesses. It is a daily fight to keep these natural born killers out of finished products. It is a war that is won through daily battles and the biggest enemy is Listeria Monocytogenes.

The first step in winning these daily battles is to know what we are fighting.

Listeria monocytogenesis a specific member of the Listeria family. It is capable of causing severe illness and even death. The mortality rate from Listeria monocytogenesis one of the highest of any known food pathogen. The Centers for Disease Control and Prevention reports that the bacteria is responsible for more than 2,000 foodborne illnesses and more than 500 deaths annually. It has been reported that Listeria is pres-ent in more than 10% of all raw milk from U.S. dairy farms. Listeriahas been found throughout the environment.

The Listeria family of bacteria is considered to be psychrotrophic (capable of survival and growth at refrigerated temperatures). Listeria is not destroyed by freezing and thrives in dairy plant environments.

In 1985, Listeria monocytogenes was identified as an emerging pathogen and the world changed for the dairy industry. At that time, there were a lot of questions (but few answers):

  1. Can we eliminate it?
  2. Where did it come from?
  3. How does it grow?
  4. Can we control it?
  5. Will sanitizers destroy it?
  6. Does it survive pasteurization?

Those questions have been answered over time.

  1. No, we probably will not eliminate it from our dairy plant environment, but we can keep it out of our products.
  2. Listeriais present in raw milk and the environment.
  3. Listeriacan grow at refrigerated temperatures and can survive freezing.
  4. Yes, through cleaning, sanitizing and good manufacturing practices (GMPs).
  5. Yes, sanitizers are effective but only on clean surfaces.
  6. No, pasteurization effectively kills Listeria.

The next step involves some reconnaissance. We have identified the enemy, now it’s time to locate it. Prior to the mid-1980s, the sanitation and bacteriological monitoring of nonproduct contact surfaces or the environment was not a high priority. In the mid-1980s, we began to understand that pathogens, like Listeria, are found in plant environments and in raw milk. Listeriais capable of attaching to equipment surfaces and forming a biofilm that protects them from chemical sanitizers.

Testing of environmental surfaces has become a standard practice for minimizing the potential for contamination of dairy products. Effective environmental sampling pro-grams require a number of decisions:

  1. Sampling protocol. Decide testing specifics and the number of samples to be tested.
  2. Testing protocol. Decide which pathogens to target.
  3. Follow-up action. Follow-up to clean and sanitize positive areas.

It is suggested that an environmental testing program divide areas into three zones:

  • Zone 1. Areas in the facility that are very close to product-contact surfaces, but not product-contact surfaces.
  • Zone 2. Areas close to the finished product/packaging area, including control panels, framework or sides of equipment.
  • Zone 3. Includes floors, drains, exteriors, in-line conveyor chains and similar places.

Swabbing and testing of 10 to 30 sites should be performed monthly, with 50% of the swabs taken from zone 1, 30% from zone 2, and 20% from zone 3. Remember, the goal is not to obtain negative results but to identify problem areas.

Time to attack

Effective cleaning and sanitizing of equipment and environmental surfaces is essential to controlling Listeria monocytogenesin dairy plants. Fortunately, Listeria monocytogenesis highly susceptible to most sanitizers if the biofilm has been completely removed by proper and effective cleaning. However, for sanitizers to be effective, all food residues and the biofilm must be removed from the bacteria attached to surfaces.

In addition, the cleaning and sanitizing program must be supported by a robust GMP program. People are a primary means of distributing Listeriathroughout the plant environment and must understand the importance of the GMP program.

Can we eliminate Listeria? Not likely, but we can win the war by controlling it through sound dairy practices. 

For More Information

Learn more about Randolph Associates Inc.’s training programs, products and technical

expertise by visiting the company website at Sign up for the following training courses:

  • HACCP Certification Course, Sept. 22 to 24
  • Implementing SQF Systems, Sep. 24 to 26

 For registration and additional information, contact Kristy Clark at 205-595-6455 or email

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