Bacterial count and SCC in milk: what tank temperature has to do with them
Brazil’s bacterial count and SCC limits as an example, why the bacterial count rises when milk is slow to cool, and why the somatic cell count tells a different story.
Two numbers decide whether a farm’s milk meets the standard and, at many dairy processors, how much it is worth: the bacterial count and the SCC. Both come from testing the bulk tank milk, but they tell different stories, and only one of them has anything to do with temperature.
What each one measures
- Bacterial count (standard plate count, SPC, also reported as total bacterial count): the number of bacteria in the milk, in colony-forming units per milliliter (CFU/mL). It measures hygiene and preservation: milking, equipment cleaning and cooling.
- SCC, somatic cell count: the number of the cow’s defense cells in the milk, in cells per milliliter. It measures udder health: the more mastitis in the herd, the higher the SCC.
Limits: the Brazilian example
Limits are set by each country’s regulation. In Brazil, regulation IN 76/2018 sets that raw refrigerated milk from an individual or communal tank must show quarterly geometric means of:
| Indicator | Limit in Brazil (IN 76) |
|---|---|
| Bacterial count (SPC) | up to 300,000 CFU/mL |
| SCC | up to 500,000 cells/mL |
The means use tests from three consecutive months, with at least one sample per month from each tank (IN 76/2018, art. 7). Check the limits and calculation method that apply in your country.
Where temperature comes in
For the bacterial count, directly. Milk leaves the cow close to the temperature at which bacteria grow fastest. Until it reaches 4 °C, they multiply; after that they grow very slowly, but they do not stop, and some bacteria actually thrive in the cold. That is why two things matter:
- The speed of cooling after each milking.
- The stability of the temperature until collection, with no rises caused by power outages or a stopped compressor.
But temperature does not make up for hygiene. Poorly washed milking equipment and a dirty tank seed bacteria that cold only slows down. A high bacterial count with a perfect cooling curve points to cleaning.
For SCC, temperature plays no part. Somatic cells do not multiply in the tank. High SCC is a herd management issue: mastitis, milking routine, pre- and post-dipping, dry cow therapy. Better cooling does not lower SCC.
What temperature data helps you tell apart
With the curve of every cooling cycle on record, the conversation with the technical advisor changes:
- Bacterial count went up and the curve got worse: the problem is refrigeration.
- Bacterial count went up and the curve is fine: the problem is hygiene.
- SCC went up: the problem is in the herd, not in the tank.
Where IoTData comes in
The milk tank kit, which records the curve of each cooling cycle and the compressor current, is in development for pilots with cooperatives and dairy processors. See milk tank monitoring.
Sources: Brazilian Ministry of Agriculture (MAPA) Normative Instruction 76/2018, art. 7 (bacterial count and SCC limits and how the means are calculated); MAPA Normative Instruction 77/2018 (cooling in direct-expansion tanks); both cited as examples of national regulation.