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. NDA’s Food Safety Laboratory is FDA accredited as a State
Central Milk Lab and analyzes these samples and reports their findings to the
state. The laboratory’s degreed microbiologists are dedicated to providing the
highest quality of testing. They maintain federal certifications for milk and
dairy testing and routinely participate in proficiency testing programs to ensure
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 0.0°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 ensures that milk from
antibiotic treated cows does not
enter the food supply.
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 Food Safety Laboratory determines the somatic cell count by direct
microscopic examination of the milk or through flow cytometry . Somatic Cell Counts above 400,000 SSC/mL (750,000 SSC/mL for sheep
and 1,500,000 SSC/mL for goats) are 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 amount bacteria
in milk. It reveals general sanitation and herd health conditions. By use of
culture technique, the standard plate count is assessed. This count must not
exceed 100,000 CFU/mL for raw milk or 20,000 cfu/mL of g for pasteurized retail
This procedure is a more specific bacterial test for the quality of the milk and is an indicator of proper sanitation. High coliform counts can be caused by poor herd hygiene, improperly washed and maintained equipment, or a contaminated water supply. Microbiological testing with Violet Red Bile containing growth media enables the microbiologist to determine the coliform count. Retail products must have a coliform count below 10/CFU/mL or g to conform to State regulations
This test is performed to ensure proper pasteurization has been performed on all retail products. A fluorometric procedure is used for the analysis and an alkaline phosphatase reading of less than 350mU/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 Present/Absent (P/A) procedure is used to detect coliform organisms in the source water used by the dairy/plant.
- 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.
- Coliforms must be “Absent” in P/A testing and the acceptable limit for the HPC test is less than 500 CFU/mL.