Milk temperature in the bulk tank: how to monitor it and when to alert
Where to place the sensor, what the cooling curve shows, how compressor current reveals a problem before the thermometer does, and which alerts are worth having without becoming a nuisance.
The tank thermometer shows the temperature right now. What decides milk quality is the temperature over time: how long the milk took to cool after each milking, and whether it stayed cold until collection. Monitoring means recording that curve and raising an alert when it departs from normal.
Where to measure
- In the milk, not on the wall. The sensor has to be immersed in the milk, away from the evaporator plate, which is much colder than the rest.
- With the agitator running. Still milk stratifies, and a single reading is misleading.
- At the minimum-volume level. Right after the first milking the tank is almost empty: the sensor has to be in the milk from the start.
What the curve shows
After each milking, the curve rises and falls. Three numbers sum up each cycle:
- Inlet temperature, right after milking.
- Time to 4 °C. Cooling times are set by each country’s regulation; in Brazil, for example, regulation IN 77 limits it to three hours in direct-expansion tanks.
- Maximum temperature until collection, which has to stay low until the truck arrives.
A healthy tank repeats the same curve every day. Time to 4 °C creeping up week after week is the typical sign of a dirty condenser or low refrigerant, long before a breakdown.
The compressor tells you the cause
A split-core current sensor, which clamps around the compressor cable without touching the installation, tells you whether the compressor is on and how hard it is working:
- Compressor off while the milk warms up: electrical fault, tripped breaker, power outage.
- Compressor running nonstop and the milk slow to cool: condenser, refrigerant, or a tank too small for the volume.
- Compressor switching on and off in short cycles: a control or pressure problem.
When to alert
An alert that goes off all the time gets ignored. What is worth an alert:
- Milk above 4 °C after the expected time following milking.
- Milk above the reception limit at any time (in Brazil, IN 77 sets it at 7 °C; check the limit that applies in your country).
- Compressor off with milk in the tank.
- Power outage at the tank.
And always on a change of state: when the problem starts and when it ends, not at every reading.
Who receives it
The farmer first, because the farmer is the one who can act before collection. Then the dairy processor’s technical team, by agreement with the farmer, because they follow milk quality and the supplier improvement program.
Where IoTData comes in
The milk tank kit, with a temperature probe, a compressor current sensor and these alerts, is in development for pilots with cooperatives and dairy processors. The network, with the DG satellite network delivering data in minutes on farms with no cellular signal, and the platform already exist. See milk tank monitoring.
Sources: Brazilian Ministry of Agriculture (MAPA) Normative Instruction 77/2018 (direct-expansion tank: 4 °C within three hours; 7 °C at reception), cited as an example of national regulation; good practices for on-farm milk cooling.