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Ask an Expert: hygienic validation of closed food processing

Closed food processes may offer food safety advantages compared to open food processing, like a better protection against external hazards. But there are also disadvantages: how do you know for sure that your closed process circuit is sufficiently clean? EHEDG Authorised Trainer Martin Barnickel shares valuable insights on how to maximise food safety performances of closed food processes by applying hygienic cleaning validation techniques.


About the Expert 

Martin Barnickel studied agricultural sciences at the Technical University Munich in Weihenstephan with a focus on dairy technology and processing. Since 1991 he has been working as a trainer and teacher for dairy managers and technicians for the Lehr-, Versuchs- und Fachzentrum für Molkereiwirtschaft (Training, Test and Competence Center for Dairy Systems) in Kempten/Germany. He also develops and designs test equipment and works on plant engineering and design as a chief project manager and shares his expertise as a seminar lecturer, author of scientific literature and as a consultant.


What’s the importance of validation to guarantee food safety? 

Martin Barnickel: “Regardless whether you are a food safety manager working for a food producer or an engineer developing components for closed food or packaging processes - there’s nothing more reassuring than thorough quantitative validation of cleaning regimes. To guarantee food safety, several physical, chemical and biological hazards need to be addressed and validated.” 


What are specific challenges for closed food processes? 

“Closed food processes are prone to a wide range of food safety hazards, such as microorganisms and their toxins, residues of previous products or cleaning and disinfection agents and lubricants, and unwanted food ingredients from previous production batches that can constitute as allergens. Therefore, all closed processes need regular and effective cleaning, with or without disinfection/sterilisation. Unfortunately, some installations are quite difficult to clean thoroughly, with potentially devastating effects ranging from minor health discomforts to food poisoning illnesses and even deaths.” 


In your publications, you speak of the ‘kinetics of contamination’. Please enlighten us.

“Let’s have a closer look at the kinetics of contamination in a very common closed food process in dairy plants: pasteurisation. In these closed food-processing systems microfilm growing and contamination often occurs at the preheating and in the heat recovery stage at temperatures under 55 degrees. A precise control and documentation of pasteurisation conditions (usually 75°C for at least 15 seconds) is an absolute prerequisite to guarantee food safety in closed food processing. In general, the rule of thumb is that no one should settle with solely applying disinfection techniques when sterilisation is technically achievable.”

Picture: Martin Barnickel (interview continues below picture)

Can you share another example with us?

“Another example of kinetics of contamination is a contamination hazard that’s triggered by a panel breakthrough that may cause contamination of heated product with pathogenic microorganisms. Breakthroughs in plate heat exchangers should be tested therefore at least twice a year. Plates should not be in use for more than 5 years. In general pasteurized products should not be processed longer than 20 hours without CIP even then when the facilities were sterilised at the beginning. Otherwise a pasteurisation resistant flora may take the upper hand after that period of time. Others hazards can arise from deteriorating hygienic conditions due to aging installations. That’s why processing facilities need to be regularly tested for cracks, cavities, dead spaces and leaks. Sterile product sometimes is processed for days without interim cleaning. To prevent a facility from becoming a source of recontamination, it should be entirely free of dead spaces, it has to be bacteria-tight and operated in a professional manner at all times.”


What are the most telling validation criteria?

“The very sensitive criteria for the effectiveness of cleaning programs is the differential TOC analysis in rinsing water. Visual cleanliness and the absence of odors and biofilms are not enough by far. It is pointless to further examine equipment that doesn’t meet these most basic validation criteria. UV light generally helps to detect traces of residual material (> 4 µg/cm²). Similarly, dyes can be used to detect unwanted residuals in the closed process line. With the help of a endoscopes difficult to access and hard-to-clean spots in plants can be visually inspected. However, in many cases, a periodic disassembly may be required as well for control purpose. Because it is nearly impossible to install anti-biofouling strategies hygienic plant design, residual free cleaning an effective sterilisation is mandatory. The applied monitoring techniques should be able to quantify the hygienic level before and during the production. Problematic biofilm formation can only be avoided by cleaning in time. Rising differential pressure can be regarded as an imprecise online early warning tool. In addition to these, biological parameters such as ATP content (a constituent of all living cells central to energy transfer), total direct cell counts (TDC), which represent the concentration of microorganisms or assimilable/total organic carbon (AOC, TOC), substances which promote microbial growth, and the biofilm formation rate (BFR) may be used for assessing the hygienic level of the plant after CIP and SIP.”


More info

Please stay tuned for a more in-depth article on this subjects by this EHEDG Subject Matter Expert on For a comprehensive overview of validation techniques for closed food processes, please download the EHEDG Guideline publications of the EHEDG Working Groups Cleaning and Disinfection and the EHEDG Working Group CIP on