Pasteurisation is the one step in a dairy where a control failure is a public-health event rather than a quality complaint. It is also the first thing an auditor examines. Automation here is bought for legal defensibility.
Why This Step Is Different
Everywhere else in the plant, a control failure costs you money. Here it can cost you your licence. The pasteurizer is where the burden of proof sits, and where a missing chart trace turns an inspection into an incident.
Which is why the argument for automating it is not efficiency. It is that you can demonstrate, for any batch on any date, that milk which did not reach temperature never went forward.
The Control Scheme
| Element | What it does |
|---|---|
| HTST hold | 72 degrees C for 15 seconds continuous. Batch or LTLT runs 63 degrees C for 30 minutes. |
| Holding tube | Residence time is a function of flow, so flow control is part of pasteurisation control, not separate from it. |
| Flow diversion valve | Milk below setpoint diverts to the balance tank. Never forward. |
| Duplex temperature | Independent control and safety recording elements on the one measurement that legally matters. |
| FDV proving | Automated divert test before production, logged with timestamp. |
Fail-safe is a design requirement, not a feature. The diversion valve must fail to divert on loss of air, loss of power or loss of signal. If it fails forward, the entire control scheme is decoration.
A Single Sensor Is a Single Point of Failure
Duplex temperature sensing means separate elements for control and for safety recording. One sensor drifting silently on the only measurement carrying legal weight is a risk no plant should run. Two elements disagreeing is itself an alarm condition.
Why Automated Proving Matters
A manual FDV proving test is the first thing dropped when the plant is behind schedule, and nobody records the omission. An automated proving test runs before production whether or not anyone remembered, and the record exists whether or not anyone wanted it to.
That is the difference between a procedure you claim to follow and one you can evidence.
Sequence
- Water run and line fill
- Sterilisation hold to temperature
- FDV proving test, logged
- Product changeover
- Production with continuous recording
- Automatic divert on any excursion, with cause and duration captured
- CIP
Retrofit Scope
- Pneumatic flow diversion valve with position feedback
- Duplex PT100 temperature elements
- PLC control with independent safety logic
- Electronic recording replacing the chart recorder
- SCADA trend and per-batch report
- Interlock design and witnessed divert testing at commissioning
Track Record
Bharuch District Co-operative β 5 LLPD with Siemens PLC. Thiruvananthapuram Regional Co-operative, Kerala β two 5 LLPD plants. Mother Dairy, Junagadh. Gayatri Dairy Products, Ahmedabad.
Why This Step Is Different From Every Other Step
Every other control loop in a dairy affects cost, yield or quality. Pasteurisation affects whether people get ill. That single fact changes what the control system has to do β it is no longer enough for it to work; it has to be able to prove it worked, months later, to somebody who was not there.
Which is why the buying argument for pasteuriser automation is legal defensibility rather than efficiency. A plant that cannot produce a temperature record for a specific batch on a specific night has no defence, regardless of how carefully it was actually operated.
The Pressure Differential Nobody Asks About
On a regenerative plate heat exchanger, raw milk and pasteurised milk are separated by a single plate. If a plate cracks or a gasket fails, the direction of leakage is decided by which side is at higher pressure.
The pasteurised side must be held at higher pressure than the raw side. Then a failure pushes pasteurised milk into raw β wasteful, but safe. Get it the wrong way round and raw milk enters the pasteurised stream with nothing downstream to catch it.
- Differential pressure monitored and alarmed, not assumed from pump curves
- Interlocked to flow diversion β loss of the correct differential is a divert condition, exactly like a low temperature
- Booster pump control designed to hold the differential across the operating range, not just at design flow
- Recorded alongside temperature, because it is part of the same safety case
What the Flow Diversion Valve Has to Prove
The FDV is the single component standing between an under-processed batch and your customers. Its behaviour on every failure mode has to be a decision, not an accident.
| Failure | Required behaviour | How it is proved |
|---|---|---|
| Milk below setpoint | Divert to balance tank | Automated divert test, logged with timestamp and duration |
| Loss of instrument air | Fail to divert position | Physical test at commissioning, witnessed and recorded |
| Loss of power | Fail to divert position | Physical test, recorded |
| Loss of control signal | Fail to divert position | Physical test, recorded |
| Loss of correct pressure differential | Divert | Interlock proven at commissioning |
| Valve fails to reach position | Alarm and hold divert | Position feedback, not command confirmation |
| Holding time reduced by flow increase | Divert | Flow interlocked to the holding tube residence time |
Note the last two. Position feedback matters because a command to move is not evidence of movement β an actuator can be told to divert and fail to do it. And holding time is a function of flow, so flow control is part of pasteurisation control rather than something separate from it.
Where Pasteuriser Automation Projects Go Wrong
- Proving tests treated as commissioning paperwork rather than a scheduled, automated, pre-production routine. Manual proving is skipped under production pressure; automated proving cannot be
- A single temperature sensor on the one measurement that legally matters. Duplex sensing β independent control and recording elements β is the whole point
- Recording on the supply side rather than at the end of the holding tube, which records an intention rather than an outcome
- Divert events logged without cause, so the record shows that something happened but not why, which is worse than useless at an audit
- Records held only on the local HMI, lost when the panel is replaced or the memory card fills
The Record an Auditor Actually Wants
- Continuous temperature profile per batch, timestamped, at the legally significant measuring point
- Every divert event β time, duration, cause, and what happened to the diverted milk
- FDV proving records, automatic and dated
- Flow record, demonstrating holding time was maintained
- Pressure differential record across regeneration
- Calibration history of the recording sensor, with as-found values
- Access log β who changed a setpoint, when, and from what
All of it exportable, retrievable in minutes, and not dependent on one person remembering where the file is. That is what replaces the circular chart nobody can find.
Common Questions
Can I automate an existing PHE and holding tube?
Usually yes. The plate heat exchanger and holding tube stay. What changes is the control layer β a pneumatic flow diversion valve with position feedback, duplex temperature sensing, PLC control with independent safety logic, and electronic recording.
What happens on power or air failure mid-run?
The flow diversion valve fails to the divert position. That is the whole point of the design β on loss of air, power or signal, milk returns to the balance tank and never goes forward. We prove it at commissioning with a witnessed test.
Does this satisfy FSSAI and NDDB requirements?
The control scheme is built to the NDDB standard for automatic pasteurizers, and the recording satisfies what FSSAI auditors ask for. Interlock design and test records are handed over as part of the documentation.
How is the FDV proving test recorded?
Automatically, before production, with a timestamp. Manual proving gets skipped under production pressure. An automated proving test cannot be skipped and cannot be backdated.
Can records be exported for an audit?
Yes β per batch, with the full temperature profile, every divert event, its duration and its cause. It replaces the circular chart recorder nobody can find when the auditor asks.
Related
Dairy Plant Automation & Upgradation Β· CIP Automation Β· FSSAI Compliance Β· Liquid Milk Processing Plant
Discuss Your Pasteurizer Automation
Tell us your PHE capacity, your current flow diversion arrangement and how you record temperature today. Our engineers will come back with a control scope, a safety interlock design and an indicative budget.