The detection, identification, cause, removal and prevention of films on dairy farm equipment are all involved in the maintenance of good quality control. Films are not only unpleasant to the eye, but in most cases can contribute to increases in bacteria counts and development of off-flavors in the milk.
The words film and biofilm are often used interchangeably. A film is a generic term that refers to the visual signs of a residue complex that negatively impacts the ability of sound cleaning and sanitizing products and procedures to work effectively. 
A biofilm is a more specific term that refers to the complex of bacteria and its’ secretions at a spot or spots in the milking or cooling system. A biofilm, combined with milk nutrients or water mineral, may lead to a film. A biofilm is more often difficult to find and may require bacterial swabbing of specific sites in the equipment followed by further laboratory diagnostic tests to identify specific bacteria involved.
Films are easily detected on equipment usually cleaned by hand, such as strainers, milk pads, milker heads and related parts including valves, pulsators, gaskets, etc. They are also readily evident on bulk tanks that are manually cleaned and on rubber or plastic parts such as inflations, air hoses and milk hoses. As a rule, the soft types of films such as gelatinous material can be seen on equipment whether wet or dry, but the hard type films such as milkstone or waterstone can only be seen when the equipment is dry.  Protein films are also more evident when the equipment is dry.
If the equipment is wet at the time of the inspection, rinsing with enough hot water to heat the equipment followed by draining will cause quick drying. Heating small items such as strainers and pails can be easily done. In examining larger equipment such as bulk tanks, the use of a window squeegee applied to the surface will quickly remove residual water and allow prompt observation.
With equipment cleaned by automatic methods, inspection of certain key points can give clues to conditions on equipment not easily accessible for inspection. Milk ports or milk inlets on the milk lines should be checked for cleanliness. If milk ports or milk inlets are not clean, it is usually due to inadequate wash slugs or leakage of milk ports or milk inlets and jetter assemblies during the wash cycle. Corrective action is to install a properly-sized, adjustable air injector in the wash system, properly adjust the air injector presently installed on the system, and/or allow more wash solution into the pipeline when washing. If milk ports or milk inlet closures do not seal tightly, air may continue to leak into such ports and/or inlets, displacing the wash solution contact action and leaving the milk ports or inlets and pipeline unclean.
This is an excerpt from the Dairy Practices Council’s Guideline #28, Troubleshooting Residual Films on Dairy Farm Milk Handling Equipment. More information can be found at the Dairy Practices Council’s website: www.dairypc.org > Guidelines > Milking Machines.

Steve Lehman is the Technical Area Supervisor for Michigan Milk Producers Association (MMPA), a milk marketing cooperative serving over 1,200 farms located in Michigan, Indiana, Ohio, and Wisconsin. Steve has over 25 years’ experience working with MMPA in the areas of farm inspection, milk quality, equipment evaluation, and facility design. He is currently serving as the Task Force V Director for the Dairy Practices Council, and resides in Ithaca, Michigan.