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Dairy and Food Testing Information

Standard Plate Count:

The Standard Plate Count (SPC) of raw milk samples gives an indication of the total number of aerobic bacteria present in the milk at the time of pickup. Milk samples are plated in a semi-solid nutrient media and then incubated for 48 hours at 32°C (90°F) to encourage bacterial growth. Single bacteria or tight clusters (e.g. chains or clumps) grow to become visible colonies that are then counted. All bacterial plate counts are expressed as the number of colony forming units (cfu) per milliliter (ml).  Aseptically collected milk from clean, healthy cows generally has SPC values of less than 1,000.

Coliform Count:

The Coliform Count procedure selects for bacteria that are most commonly associated with manure or environmental contamination. Milk samples are plated on a selective bacterial media that encourages the growth of coliform bacteria, while preventing the growth of others. Though coliforms are often used as indicators of fecal contamination, there are strains that commonly exist in the environment. Generally, counts >50 would indicate poor milking hygiene or other sources of contamination.

Somatic Cell Count (direct microscope):

The term "somatic" means "derived from the body". The majority of somatic cells are leukocytes (white blood cells) - which become present in increasing numbers in milk usually as an immune response to a mastitis-causing pathogen - and a small number of epithelial cells, which are milk-producing cells shed from inside of the udder when an infection occurs. The cell count for "normal" milk is nearly always less than 200,000 cells/ml (lower for first lactation cows). Higher counts are considered abnormal and indicate probable infection. Higher counts are also associated with decreased production. The Somatic Cell Count (SCC) is a main indicator of milk quality-- having implications for its keeping abilities, its taste and how well it can be made into other dairy products such as yogurt or cheese. Goats tend to have naturally higher SCC (when cells are counted using the same method traditionally used on cow milk), with standards being <1,000,000 on the high end.

Staphylococcus aureus:

Staphylococcus aureus (Staph) causes one of the most common types of chronic mastitis. The main reservoir for S. aureus is the infected udder. Bacteria are spread from the infected quarter to other quarters and to other cows primarily through milk from infected animals contaminating milking machines, milker’s hands, towels, or other items used in the milk parlor during milking. 

Antibiotic Residue Testing:

All samples received can be tested for antibiotic residue as well. 

Alkaline Phosphatase Testing (ALP):

Milk subjected to pasteurization should show a negative phosphatase reaction immediately following heat treatment. This test reveals the efficacy of pasteurization practices and can be a useful tool to troubleshoot equipment failures. 




Reference: Murphy, S. C. 2008. Sources and Causes of High Bacteria Counts-An Abbreviated Review.
Cornell University, Milk Improvement Program, Department of Food Science.


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