Cold Room Temperature Monitoring: What an Audit Asks For

For a HACCP or BRCGS audit, cold room temperature monitoring has to demonstrate four things: that measurement is continuous, that the sensor is calibrated, that someone received the alarm when it went out of range, and what was done with the product. The sensor is the cheap part; what gets audited is everything else.

Data logger or continuous monitoring? #

The data logger proves what happened; continuous monitoring lets you act before you lose the product. Many plants use both: continuous in cold rooms and tunnels, data loggers in trucks and in temperature distribution studies.

What does an audit ask for? #

• HACCP: if temperature is a critical control point, it must be monitored against its critical limit at the frequency defined in the plan, and every deviation must have its corrective action recorded.
• BRCGS: temperature-controlled storage must have recording equipment with alarms, or a system of recorded manual checks at a frequency that allows action before the limit is exceeded. Records must carry date, time and result, and someone must review them.
• Chile's Food Sanitary Regulation (Reglamento Sanitario de los Alimentos): frozen foods are kept at −18 °C and, during transport and retail, brief rises are tolerated as long as they do not exceed −12 °C.

An auditor's question is rarely "do you have a sensor?". It is "show me what happened the night of the power outage and who saw it."

Where do the sensors go? #

Not wherever is convenient to wire. Before mounting them, it pays to do temperature mapping of each cold room, with several data loggers over a few days, to find:

• the warmest point, which is usually near the door or far from the evaporator;
• the areas where product spends the most time;
• the effect of defrost cycles and door openings.

The permanent sensor goes at the point most representative of the risk, which is normally the warmest one. In large cold rooms, one is not enough. In freezing tunnels it is also worth measuring product temperature, because the air reaches setpoint long before the core of the piece does.

How is it calibrated? #

With a calibrated reference thermometer, comparing readings at the same point and recording the difference. The audit asks for the instrument inventory, the calibration date of each one and what is done when one falls out of tolerance.

At Ditzler, the IQF tunnel temperature measured by iGromi was checked against a reference standard with a 0.05 °C difference. That is the number you show when someone asks whether the sensor can be trusted.

Which alarms should you configure? #

• Temperature above the limit, with a delay so it does not trigger on every door opening or scheduled defrost.
• Accumulated time out of range, not just the peak.
• A sensor that has stopped reporting, or a communication loss.
• Power loss to the cold room.
• Escalation: if the shift does not acknowledge the alarm within a set time, it goes to the supervisor and then to maintenance.

An alarm that reaches a phone nobody looks at is the same as having no alarm. What gets audited is the acknowledgment: who saw it and at what time.

Wi-Fi, cable or radio? #

Cold rooms are metal boxes with insulated panels, and Wi-Fi usually gets through them poorly. Before buying Wi-Fi sensors, measure the signal inside each cold room with the door closed. The alternatives are cable (RS-485 or Ethernet), long-range radio such as LoRa, or cellular. We compare them in the guide to industrial telemetry.

What to ask the vendor before you buy #

1. Does the sensor come with a calibration certificate, and how is it recalibrated?
2. What happens to the data if the internet goes down? Is it stored and sent later?
3. How does someone find out that a sensor has stopped reporting?
4. Can the corrective action be recorded alongside the alarm?
5. Who can modify or delete a record, and is there a trail?
6. Can I export all the data without depending on the vendor?
7. Does it read the refrigeration controllers I already have, or only its own sensors?
8. Does it work inside my cold rooms? Ask for a test in the worst one.

What does iGromi do? #

We measure calibrated temperature in cold rooms, tunnels and processes, together with production counts and energy, on the same dashboard and on the equipment the plant already has. The case in production is Ditzler. We do not replace the quality manager and we do not certify: we deliver the record and the alarms so your HACCP plan is carried out every shift. How this fits into full traceability is covered in the guide to traceability in food plants, and how the cold chain breaks outside the plant, in the digital cold chain.

Frequently asked questions #

How often should temperature be recorded?

Each plant's HACCP plan defines it based on risk. With automatic monitoring it is common to record every few minutes in tunnels and critical processes and somewhat less often in storage rooms.

Should you measure the air or the product?

In storage rooms, air at the warmest point is usually enough. In freezing tunnels and blast chilling it is worth measuring the product too, because the product is what tells you whether the process did its job.

Is a consumer Wi-Fi temperature and humidity sensor good enough?

For a small storeroom, it may be. For an audit it usually falls short: it rarely comes with a calibration certificate, it does not warn you when it stops reporting, and Wi-Fi fails inside cold rooms.

Do you also need to measure humidity?

It depends on the product. For fresh fruit and in some processing rooms humidity matters as much as temperature; for frozen goods, much less.