When a shipment is running late, pre-cooling is the easiest step to skip. The body is loaded, the door is shut, the road is clear, and warm air inside bothers nobody for the first half hour. Turkey's Ministry of National Education module on refrigerated vehicles describes this step with a number attached.
The rule itself
According to the module, before goods are loaded the refrigeration system must be run until the body comes down to the product's carriage temperature. Where there is no time for that, the temperature inside the body may be at most 4 °C above the product's carriage temperature.
Four degrees is a tolerance, not a target. For a body working in a -18 °C regime that means a ceiling of -14 °C, and frozen goods loaded at that temperature spend their first minutes eating into the allowance.
Why the vehicle cannot do this job. The module gives the reason plainly: refrigerated vehicles used in transport are not designed to pre-cool or to freeze at low temperatures. If the vehicle cannot absorb the heat coming from the product within the required time, the food starts to spoil.
The structural materials of the body carry heat of their own. Pre-cooling removes that too; without it the refrigeration system is pulling heat from the walls as well as from the load.
That reading belongs on the first line of the record for the cold chain at a distribution centre.
The second function of pre-cooling
The module lists a side benefit: pre-cooling the body makes it possible to identify a vehicle with a faulty refrigeration system in advance. A unit that will not run before loading will not run after it either, and seeing the difference on the dock is cheaper than seeing it on the road.
Pre-cooling the product is a separate job
The same section of the module describes meat and fish being pre-cooled after slaughter, and fruit and vegetables being cooled immediately after harvest. That is a different task from pre-cooling the body and it happens at the plant. Both have to be finished before the moment of loading.
Three lines to check on the dock
- Was the internal temperature measured, and how far is it from the product's carriage temperature
- Did the unit run through the pre-cooling, and for how many minutes
- What temperature was the product at when it left the store
A temperature measured after loading no longer says anything about what happened before it.
