Milk and Dairy Product Testing

The Nevada Department of Agriculture has strict guidelines for the monitoring of the milk and dairy industry. Samples are taken monthly to ensure adherence to these regulations and the Food and Drug Administration food safety program. The University of Nevada Reno State Public Health Lab analyzes these samples and reports their findings to the state. The laboratory’s degreed microbiologists are dedicated to providing quality testing. They maintain state certifications for milk and dairy testing and routinely perform proficiency testing to insure the public has safe dairy products.  


Testing Procedures and Their Significance

State Environmental Health Specialists are responsible for collecting monthly samples from dairies and retail milk plants for analysis. These samples are carefully monitored to arrive in the lab in a timely fashion (48 hours or less) and with a temperature of 0°C to 4.4°C maintained from collection until arrival in the lab. In order for dairies and plants to avoid off grade penalties and/or interruption in production, these samples must meet State requirements on the following tests:


Milk containing antibiotics cannot be used for human consumption. The use of milk drug residue assays insures that milk from antibiotic-treated cows is not marketed.

Somatic Cell Count

This test measures the amount of white blood cells and tissue cells in a milk sample. All milk contains some of these cells. High counts indicate a herd health problem and directly affect milk production and income. The microbiologist determines the somatic cell count by direct microscopic examination of the milk. A count above 400,000 is reported to the State and will cause a restriction on the sale of that dairy's milk. 

Standard Plate Count

This is a basic quality test that is a measure of the bacteria in milk. It reveals general sanitation and herd health conditions. By use of culture technique (agar, incubation) the SPC count is assessed. This count must be less than or equal to 100,000 ml for raw milk or 20,000/g or ml for retail products.


This procedure is a more specific bacterial test for the quality of the milk. It is an indicator of proper sanitation. High counts can be caused by poor herd hygiene, improperly washed and maintained equipment, or a contaminated water supply. Microbiological testing with Violet Red Bile agar enables the microbiologist to determine the coliform count. Retail products must have a coliform count below 10/g or ml to conform to State regulations. This test is not State regulated for raw milk, but it can alert dairymen to potential problems. 


This test is performed to insure proper pasteurization has been performed on all retail products. A flurometric procedure is used for the analysis and an alkaline phosphatase reading of less than 350mμ/L must be obtained.

Dairy Water Testing

To be suitable for use in dairy operations, water must be of a safe, sanitary quality and free of microorganisms that could initiate spoilage. Three procedures are used in the testing of dairy waters to insure the quality of the water:

  • The Coliform MPN procedure is used to detect coliform organisms in the source water used by the dairy/plant.
  • Membrane Filtration (MF) technique is used to detect coliform organisms in glycols and chill waters.
  • Water Heterotropic Plate Count (HPC) is used to further analyze the quality of the dairy operation water. This can be done on both source and glycol/chill waters. Through a culture technique (agar, incubation) a count is assessed.

Acceptable limits are "no coliforms found" for the MPN and MF procedure, and less than 500 CFU’s/ml for the HPC test.