Milk cooling tank failure on a Saturday night

Dairy farm with 280 milking cows and a 6,000 L cooling tank. On Saturday afternoon, 4,200 L are milked that must stay below 4 °C until Monday's 08:00 pickup. EU regulation (Reg. 853/2004) sets 6 °C max for milk stored >2 h after milking; any deviation forces the tanker to be rejected.

Saturday at 22:18 the tank compressor fails due to a stuck expansion valve. The tank starts warming. Without an alarm, the Sunday milker would discover it at 06:00 with milk already at 8-9 °C — automatic discard.

Aviot monitors tank temperature with a submerged PT100 probe plus the cooling unit panel contact. Configuration:

• Tank reading every 30 seconds.
• Pre-warn at 4.5 °C.
• Critical alarm at 5.0 °C.
• Instant alarm if the cooling panel reports a fault (current, phase, pressure).

At 22:18:30 the panel contact flags an anomaly. Aviot calls the farmer. Picked up at 22:19. The farmer checks the compressor is stopped and rings the on-call refrigeration service (external contract).

The refrigeration tech arrives at 23:35. Diagnosis: blocked expansion valve. Replacement: 1 h 50 min. Compressor back at 01:25.

Total time the tank was without active cooling: 3 h 7 min. Maximum temperature reached: 4.4 °C (the critical alarm never fired thanks to thermal inertia and the fact the milk was already at 3.2 °C).

Sunday morning reading: 3.6 °C. Monday at 08:00 (pickup): 3.4 °C. Tanker accepted without incident, no rejection.

Aviot's detailed history served as evidence for the dairy industry buyer that temperature never crossed the legal limit. Without an alarm, those 3 h 7 min would have stretched to 8+ hours and the tanker would have been 100% rejected.

Incident cost: refrigeration tech bill (~€430). Without Aviot: tanker discard ~€9,500 plus partial Monday milk also compromised.