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The protein of milk residue can be quantitated to evaluate a cleaning process by monitoring the accumulation of protein in a test-wash solution. The test for protein is based on precipitation of hard water cations with orthophosphate and flocculation with a coagulant for rapid sedimentation of the protein. The sediment is collected on filter paper and stained with xylene brilliant cyanin G. Color reaction on the filter paper is proportional to protein content of the original test solution and is estimated visually. For more precise quantitation, the stain is released into a solution for optical measurements. The lower limit of sensitivity is approximately 34 ng of protein per ml in the original caustic test wash. Quantity of added protein to a caustic test wash and optical density of the final test dye solution showed a correlation coefficient of .99. The method developed in this work should be useful in studying clean-in-place regimen to evaluate commercial practices and fundamentals of the processes.