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Microbial contamination in the food and beverage manufacturing industry is a serious concern. Since this type of contamination directly affects the safety of the products, manufacturers must consider all potential sources of contamination. Contaminated compressed air, ambient air, or surfaces can negatively impact the safety and quality of food and beverage products. 

Microorganisms are ubiquitous; therefore, not all microorganisms are necessarily harmful or unexpected in these facilities. Microbes are found everywhere, in almost all environments. Some microorganisms, known as "indicator organisms," are of particular concern to facilities and must be carefully monitored. Indicator organisms are groups of organisms that reflect the general condition of a food or an environment where food is processed. Testing for indicator organisms is a way to monitor or validate sanitation and process control.1

Since microorganisms are capable of thriving in all kinds of locations, including often-overlooked places like compressed air systems, it is essential to regularly test for contamination in these distribution lines and production environments. A serious contamination problem could put products at risk. 

How Microbial Testing Works

ISO 8573, the international compressed air testing standard, dictates that sampling for microbes in compressed air should be completed with an impaction sampler. This is the best way to achieve qualitative and quantitative results. Once sampling is complete, the agar plates are incubated for 10 days and then analyzed at an accredited laboratory. 

Ambient air and surfaces can be tested according to ISO 14698 or custom specifications. Routinely monitoring surfaces and ambient air can be completed with settle plates, impaction samples, surface swabs, or contact plates. Sampling type will depend heavily on the needs and risks per the unique facility. 

Analysis begins with enumeration—performing a total plate count. If no growth is detected, then <1 CFU will be reported. This indicates that cleaning and sanitation processes are effective. If CFUs appear on the plates, then further analysis can be performed to aid in the identification of the microorganism. 

Gram's staining provides more information about the microbes in question. The stain color and shape of the organism can reveal information about whether or not the organism is one of concern for the facility. Table 1 shows Gram's staining information for different pathogens. 

If the Gram's staining results do not eliminate microbial concern, then phenotypic identification can be performed to identify the genus and species. Each microorganism species utilizes, metabolizes, and catalyzes a unique "fingerprint" of chemical reactions and tolerances to differentiate itself from other species. 

Results and Troubleshooting

Indicator organisms in food are typically much easier to test for than pathogens themselves, and can be used to evaluate both the quality of the food product (i.e., for spoilage) and the safety of the environment.2 Once the data is reported, the results can be used to help determine the source of contamination. 

Areas of contamination in compressed air systems can generally be attributed to the following: the quality of air drawn into the compressor, wear particles, and storage and distribution systems.3If a compressed air system is not properly maintained and filtered, it too can become contaminated with microbial growth.3 Depending on the location of the intake air, if the compressed air test results reveal microbial contamination outside of acceptable limits, then it is important to make remediation attempts to protect the end products. 

Testing the ambient air in controlled environments is critical to ensure that procedures and protocols are working as expected. Regular surface testing can reveal areas of concern or places where protocols may be improved.

Trend analyses and detailed record-keeping are essential in tracking down and troubleshooting contamination. Microbes are particularly versatile, so knowing which protocols or procedures are currently in place and outlining any recent changes to the workflow can be helpful. For example, bacteria like Listeria have characteristics that permit it to survive and effectively compete with other microbes in food processing environments.4

Protocol fatigue can affect all individuals. Masks slip, hands go unwashed, and sanitization protocols slack over time. It is the responsibility of each facility to keep cleaning protocols and procedures up to standard and implemented correctly. Often, microbial contamination points to a reduction in cleaning or sanitization procedures. In compressed air systems, it can also point to other types of contamination. Microbes thrive in wet, warm environments. Water or oil contamination in a system can provide an excellent environment for microorganisms to grow and spread. Particle contamination can provide fuel for microbial growth, as some microbes can consume them as they grow. It is essential to consider a facility's filtration, dryers, and distribution system when considering paths for remediation and troubleshooting contamination.

Implementing a Monitoring Plan

Regular monitoring of a compressed air system is the best way to ensure that quality is maintained, regardless of seasonal changes or maintenance schedules. Compressed air lines are dynamic and must be routinely tested for quality.

Quarterly testing of compressed air systems is recommended. It is best to test as close to the point of use as possible, as this will provide the most accurate representation of the air quality that is directly or indirectly impacting products. Trace Analytics can help outline a thorough monitoring plan for all contaminants in compressed air systems. Download this document to learn more. 

Ambient air and surfaces should be regularly monitored, as well. The monitoring of these environments is usually dictated by the level of risks or hazards anticipated by the facility. Although some facilities have onsite laboratories, third-party analysis can help confirm the results and allow facilities to move forward with confidence that their quality procedures are in place and effective. 

Working with a third-party accredited laboratory is the best way to ensure accurate results, proper documentation, and appropriate sampling techniques. Partner with the testing experts at Trace Analytics today. 


1 "Testing for indicator organisms and pathogens." 3M Food Safety News. July 31, 2019.

2 "Why uncovering indicator organisms in food safety monitoring is vital." Barrow-Agee Laboratories. December 17, 2021.

3 Sandoval, M. "Presumptive identification of microbes in food grade air." International Food Safety and Quality Network. March 24, 2019.

4 Kornacki, J. "Controlling Listeria in the Food Processing Environment." Food Technology Magazine. IFT. November 1, 2005.