Turbidity in post-harvest wash water: Monitor and change when needed

Excessive turbidity may hamper efforts to effectively maintain sanitary post-harvest wash water. Keep monitoring this very important post-harvest wash component.

Turbidity in post-harvest wash water is one of three major factors that need to be monitored to ensure effectiveness of sanitizer in wash water. Along with the wrong pH and inadequate free sanitizer, excessive turbidity may hamper efforts to effectively maintain sanitary post-harvest wash water. Excessively turbid water can either be from organic sources like plant particles and “juices,” or inorganic sources like soil. Excessive turbidity will consume the fast-acting oxidizers and interfere with testing of sanitizer levels, making it ineffective. In addition, the Food Safety Modernization Act also requires growers to monitor turbidity in post-harvest wash water.

Turbidity is a measure of the clarity of water. In lakes and streams, environmental scientists use a tool called a Secchi disk to measure turbidity. The disk itself has a high contrast pattern on it, divided in quarters and colored alternating black and white. The disk is dropped into a water body and lowered into the water until the scientist can’t see the pattern. The depth is recorded and it is used as a comparison with other water bodies.

A similar process has been devised for post-harvest wash water by Trevor Suslow of the University of California-Davis. A disk, obtainable by calling 517-788-4292, can be placed at the bottom of a clear polycarbonate cylinder that is at least 18 inches deep. The cylinder is then filled with wash water from the use that needs tested. If the outer cross (labeled 300 NTU) is unable to be seen, it is time to change the wash water on account of excessive turbidity.

With most cases in food safety, just performing practices is not enough. A practice that has not been recorded never happened. There needs to be an accompanying SOP on how to implement the practice and a record of performance.

If you have specific questions about turbidity or have difficulty tailoring GAPs to your farm, contact Michigan State University Extension’s Agrifood Safety Work Group at .(JavaScript must be enabled to view this email address) or 517-788-4292. For more information on turbidity, request AFSM 043-01.

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