Part of the reason that plants perform incorrect tests is due to misunderstandings, either about the tests and/or what the results indicate. For example, coliforms are common waterborne contaminants and most species are completely harmless. However, thanks to the media and pseudo-scientists, there are many people who believe that coliforms are deadly rather than a potential index organism of poor sanitation.
Another common mistake is using the wrong media for testing or failing to modify a medium so that it will detect potential problems. Culturing tomato paste samples on something like nutrient agar or plate count agar, for example, will frequently reveal a high bacteria count. Yet, this is a product that may contain aerobic sporeforming bacteria, which will grow on a basic medium. That's why, in this example, orange serum or a modified juice agar is a better choice. Ultimately, the key point to remember is that media may need to be modified with sugars, acids, salts or other components to mirror the food system and provide a better picture of what is happening.
Finally, remember to evaluate which chemical and physical tests are appropriate for your facility. Today's food and beverage manufacturers have access to many types of rapid tests. There are quick tests for allergens, such as peanuts, soy, milk, proteins and mycotoxins, as well as a wide range of tests for measuring adenosine triphosphate (ATP). However, some companies do not fully understand how these tests should be used. (For example, the allergen and mycotoxin tests are meant to be screening tests.) If you use one of these tests, take the time and invest the money to properly validate the test. Find out if the foods or environment being tested are susceptible to false positives or negatives. Can the test be used with your plant's food system? The test supplier should be able to provide you with this information.
The bottom line? Do your homework before designing a testing program. Consider the microbiological and chemical parameters and obtain the information you need to ensure the tests perform properly and correlate with official methods. Ultimately, validating the tests and the systems in which they are used is your responsibility. Remember that the results will be used to verify that your products are safe. Isn't that enough of a reason to do your homework?